Chapter V: Muscles of the Leg and Foot (13)

I. The =cœliac artery= or =axis= (A. cœliaca) is an unpaired vessel, usually half an inch or less (ca. 1 cm.) in length, which arises from the ventral aspect of the aorta at its emergence from the hiatus aorticus. It divides on the dorsal surface of the pancreas into three branches—the gastric, hepatic, and splenic.

1. The =gastric artery= (A. gastrica sinistra) passes downward and forward in the gastro-phrenic ligament, gives off œsophageal and pancreatic branches, and divides above and behind the cardia into anterior and posterior branches.

(_a_) The =anterior branch= (Ramus cranialis) crosses the lesser curvature just to the right of the cardia and ramifies on the parietal surface of the stomach. The branches pursue a flexuous course toward the greater curvature and anastomose with the short gastric arteries and the gastric branch of the hepatic artery.

(_b_) The =posterior branch= (Ramus caudalis) is distributed in a similar fashion on the visceral surface.

(_c_) The =œsophageal branch= (Ramus œsophageus) passes through the hiatus œsophageus into the thoracic cavity above the œsophagus and anastomoses with the œsophageal branch of the broncho-œsophageal artery.

FIG. 449.—PLAN OF CHIEF BRANCHES OF ANTERIOR MESENTERIC ARTERY OF
HORSE.

_1_, Stump of anterior mesenteric artery; _2_, stumps of arteries of
small intestine; _3_, external cæcal artery, _4_, internal cæcal
artery; _5_, ileal artery; _6_, ventral colic artery; _7_, dorsal
colic artery; _8_, middle colic or first artery of small colon.
]

The gastric artery often arises by a common trunk with the splenic.
The two terminal branches may arise separately, or the anterior from
the splenic and the posterior from the hepatic. The œsophageal branch
often arises from the splenic or the posterior gastric.

FIG. 450.—DISSECTION OF SUBLUMBAR REGION, PELVIC INLET, AND INNER
SURFACE OF THIGH OF HORSE.

_Blood-vessels_: _1_, Aorta; _2_, posterior vena cava; _3_, hepatic;
_4_, gastric; _5_, splenic; _6_, _7_, renal; _8_, anterior
mesenteric; _9_, arteries of small intestine; _10_, ileo-cæco-colic;
_11_, dorsal colic; _12_, artery of small colon; _13_, posterior
mesenteric; _14_, external iliac; _15_, internal iliac; _16_,
circumflex iliac; _17_, _19_, anterior and posterior branches of
_16_; _18_, anastomosis with intercostals; 20, spermatic; _21_,
cremasteric; _22_, lateral sacral; _23_, internal pudic; _24_,
umbilical; _25_, femoral; _26_, deep femoral; _27_, anterior
femoral; _28_, branch to gracilis; _29_, saphenous.

_Lymph vessels and glands_: _a_, Lymph vessels; _b_, lumbar glands;
_c_, internal iliac glands; _d_, external iliac glands; _e_,
precrural glands; _f_, deep inguinal glands (position indicated by
dotted line).

_Nerves and ganglia_: _1_, _2_, Left and right cœliaco-mesenteric
ganglia; _3_, posterior mesenteric ganglion; _4_, connection between
_1_ and _2_; _5_, connection between hepatic and splenic nerves;
_6_, _7_, connections between anterior and posterior mesenteric
ganglia; _8_, splanchnic nerve; _9_, lumbar trunk of sympathetic;
_10_, pelvic branches of posterior mesenteric ganglion; _11_,
internal spermatic nerve; _12_, last thoracic nerve; _13_,
ilio-hypogastric nerve; _14_, anastomosis between _13_ and _15_,
ilio-inguinal nerve; _16_, _17_, cutaneous and muscular branches of
_15_; _18_, _19_, muscular and scrotal branches of external
spermatic nerve; _20_, external cutaneous nerve of thigh; _21_,
femoral nerve; _22_, saphenous nerve; _23_, branch of _22_ to
sartorius.

_A_, Cut surface of obliquus abdominis externus; _B_, cut surface of
obliquus abdominis internus; _C_, depression due to disappearance of
fat in interval between outer border of psoas major and iliacus;
_D_, thick part of iliac fascia which extends from tendon of psoas
minor to external angle of ilium; _E_, superficial fascia of flank;
_F_, internal inguinal ring; _G_, external inguinal ring; _H_,
patella; _I_, femoral canal; _J_, semimembranosus; _K_, suspensory
ligaments of penis; _L_, cross-section of penis; _M_, stump of
spermatic cord; _N_, ilio-psoas; _O_, tensor fasciæ latæ; _P_, _P_,
extremities of external angle of ilium; _Q_, remains of iliac
fascia; _R_, ilio-lumbar ligament or deep layer of lumbo-dorsal
fascia; _S_, line of attachment of gastro-pancreatic fold; _T_,
tendon of right crus of diaphragm; _U_, right crus; _V_, aorta at
hiatus aorticus; _W_, left crus of diaphragm. The position of the
kidneys is indicated by dotted lines. (After Schmaltz, Atlas d.
Anat. d. Pferdes)
]

2. The =hepatic artery= (A. hepatica) is larger than the gastric. It passes forward to the right and ventrally on the dorsal surface of the pancreas, covered by the gastro-pancreatic fold, crossing obliquely under the vena cava, and reaches the inner border of the portal vein. It divides into three or four branches which enter the portal fissure of the liver and ramify within the gland with the portal vein and the hepatic duct. It gives off the following collateral branches:

(_a_) =Pancreatic branches= (Aa. pancreaticæ) are given off as the artery crosses the pancreas, in which it is partly embedded.

(_b_) The =pyloric artery= (A. gastrica dextra) arises above the first curve of the duodenum. It descends to the pylorus, sending branches to the first part of the duodenum and the pylorus, and anastomoses with the gastric and right gastro-epiploic arteries. It may arise from the gastro-duodenal.

(_c_) The =gastro-duodenal artery= (A. gastroduodenalis) passes to the second curve of the duodenum and divides into the right gastro-epiploic and the pancreatico-duodenal. The =right gastro-epiploic artery= (A. gastroepiploica dextra) crosses over the posterior surface of the duodenum and enters the great omentum, in which it runs to the left, parallel with the greater curvature of the stomach. It gives branches to the latter and to the omentum and forms an anastomotic arch with the left gastro-epiploic artery. The =pancreatico-duodenal artery= (A. pancreaticoduodenalis) divides into pancreatic and duodenal branches. The former (Ramus pancreaticus) supplies the middle part of the pancreas and is often replaced by a number of variable twigs. The duodenal branch (Ramus duodenalis) passes to the right along the lesser curvature of the duodenum and anastomoses with the first branch of the anterior mesenteric artery.

3. The =splenic artery= (A. lienalis) is the largest branch of the cœliac. It passes to the left (with the large satellite vein) on the left extremity of the pancreas and across the saccus cæcus of the stomach. Entering the suspensory ligament of the spleen, it runs in the hilus of the spleen to the apex, beyond which it is continued as the left gastro-epiploic. It gives off the following branches:

(_a_) =Pancreatic branches= (Rami pancreatici) to the left extremity of the pancreas.

(_b_) =Splenic branches= (Rami lienales), which plunge into the substance of the spleen.

(_c_) =Gastric branches= (Aa. gastricæ breves), which pass in the gastro-splenic omentum to the greater curvature of the stomach, where they bifurcate and anastomose with the gastric arteries.

(_d_) The =left gastro-epiploic artery= (A. gastroepiploica sinistra) is the continuation of the splenic artery. It passes to the right in the great omentum, parallel with the greater curvature of the stomach, and anastomoses with the right gastro-epiploic. It gives off branches to the greater curvature of the stomach, and twigs to the omentum.

II. The =anterior= or =great mesenteric artery= (A. mesenterica cranialis) arises from the ventral face of the aorta at the first lumbar vertebra. It is a large unpaired trunk, about an inch (ca. 2 to 3 cm.) in length, which passes ventrally between the vena cava and the left adrenal into the root of the great mesentery, when it divides into three branches—left, right, and anterior.[165]

1. The =left branch= gives off at once about fifteen to twenty =arteries of the small intestine= (Aa. intestinales).[166] These come off close together and pass in divergent fashion between the layers of the great mesentery, each dividing into two branches which anastomose with adjacent branches to form a series of arches. In the anterior part of the series secondary arches are formed by the union of branches given off from the primary set of arches. From the convex side of these arches terminal branches pass to the wall of the small intestine, in which they ramify and form a vascular network. They are accompanied by satellite veins and by nerves and lymph vessels. The first artery anastomoses with the pancreatico-duodenal, and the last with the ileal branch of the great mesenteric artery. Branches are supplied to the mesenteric lymph glands.

2. The =right branch= (A. ileo-cæco-colica) might be regarded as the continuation of the trunk. It runs downward and a little forward and to the right and gives off the ileal, the two cæcal, and the ventral colic arteries.

(1) The =ileal= or =ileo-cæcal artery= (A. ilea) passes in retrograde fashion along the terminal part of the ileum and unites with the last branch of the left division.

(2) The =external= or =inferior cæcal artery= (Ramus cæcalis lateralis) passes between the cæcum and the origin of the colon and runs on the external muscular band of the cæcum to the apex, where it anastomoses with the internal artery. Besides numerous collaterals to the cæcum, it gives off the artery of the arch, which passes along the lesser curvature of the base of the cæcum and runs on the outer face of the origin of the great colon.

(3) The =internal= or =superior cæcal artery= (Ramus cæcalis medialis) passes along the inner band to the apex of the cæcum, where it anastomoses with the external cæcal artery.

(4) The =ventral=, =right=, or =direct colic artery= (A. colica ventralis) runs along the opposed surfaces of the ventral (first and second) parts of the great colon to the pelvic flexure, where it unites with the dorsal colic artery. It supplies the ventral parts of the great colon and sends a branch to the base of the cæcum.

3. The =anterior branch= divides after a very short course into the dorsal and middle colic arteries.

(1) The =dorsal=, =left=, or =retrograde colic artery= (A. colica dorsalis) is a large vessel which passes along the dorsal (fourth and third) parts of the great colon to the pelvic flexure, where it joins the ventral colic artery.

(2) The =middle colic artery= or =first artery of the small colon= (A. colica media) is a much smaller vessel which passes to the origin of the small colon, enters the colic mesentery, and forms an arch by joining the first branch of the posterior mesenteric artery close to the lesser curvature of the bowel. It sends an anastomotic branch to the dorsal colic artery.

III. The =renal arteries= (Aa. renales), right and left, are relatively large vessels which arise from the aorta near the anterior mesenteric. The =right artery= is the longer of the two. It crosses over the dorsal surface of the vena cava to the right and somewhat forward. At the hilus it divides into several (five to eight) branches; some of these enter the gland at the hilus, while others pass to the ventral surface and enter there. The =left artery= is short and usually arises a little further back; it passes directly outward to the kidney and is then disposed like the right one. Small collateral branches are supplied to the ureters and the adrenals. The latter also receive small vessels directly from the aorta. The distribution within the kidney has been described.

Variations in the renal arteries are frequent. Two or more arteries
may occur on one or both sides. Accessory arteries are more common on
the left side and usually enter the posterior pole of the gland. They
may arise from the aorta, the external iliac, or the circumflex iliac
artery.

IV. The =posterior= or =small mesenteric artery= (A. mesenterica caudalis) is an unpaired vessel which arises from the ventral face of the aorta at the fourth lumbar vertebra, _i. e._, about five or six inches (ca. 12 to 15 cm.) behind the origin of the anterior mesenteric artery. It is much smaller than the latter and supplies the greater part of the small colon and rectum. It descends in the colic mesentery and divides into two branches. The anterior branch (A. colica sinistra) gives off three or four arteries which divide and form anastomotic arches close to the bowel. The first arch is formed by union with the middle colic branch of the anterior mesenteric. The posterior branch or anterior hæmorrhoidal artery (A. hæmorrhoidalis cranialis) passes backward in the upper part of the mesentery and the mesorectum and terminates near the anus by anastomosing with the internal pudic artery. Three or four of its anterior collateral branches form arches.

V. The =spermatic arteries= (Aa. spermaticæ internæ), right and left, are long slender arteries which arise from the aorta near the posterior mesenteric and supply the testicle and epididymis. Each passes backward in a narrow fold of peritoneum (Plica vasculosa) to the internal inguinal ring and descends through the inguinal canal to the scrotum. In the canal and scrotum it pursues a very flexuous course in the anterior border of the spermatic cord, surrounded by the pampiniform plexus of veins, and associated closely with the spermatic nerves and lymphatics and unstriped muscle-fibers. It passes between the epididymis and testicle, runs in flexuous fashion along the attached border of the latter, turns around the posterior pole, and runs forward on the free border to the anterior pole. The largest branches arise from its ventral part, pass tortuously up either side of the gland embedded in the tunica albuginea, and give off fine branches to the gland substance. Small collateral branches are detached to the ureter and the spermatic cord.

The =utero-ovarian arteries= in the female correspond to the preceding vessels, but are much shorter. Each is placed in the anterior part of the broad ligament of the uterus and divides into ovarian and uterine branches. The =ovarian branch= (A. ovarica) pursues a flexuous course to the ovary, which it supplies. The =uterine branch= (A. uterina cranialis) passes to the concave border of the cornu of the uterus, which it supplies, anastomosing with the uterine artery.

VI. The =lumbar arteries= (Aa. lumbales) are in series with the intercostal arteries and have a similar origin and distribution. There are usually six pairs of lumbar arteries, of which five arise from the aorta and the sixth from the internal iliac or the lateral sacral at the junction of the last lumbar vertebra and the sacrum. Each passes across the body of a lumbar vertebra to the intertransverse space, gives branches to the sublumbar muscles, and divides into dorsal and ventral branches. The =dorsal branch= (Ramus dorsalis), the larger of the two, passes upward to ramify in the extensor muscles of the spine and the skin of the loins; it gives off a =spinal branch= (Ramus spinalis) which comports itself like the corresponding branch of an aortic intercostal artery. The =ventral branch= (Ramus ventralis) runs outward in the intertransverse space, passes between the transversus and obliquus internus abdominis, gives branches to these muscles, and ends in the obliquus externus, the panniculus, and the skin of the flank.

FIG. 451.—DISSECTION OF PELVIS, THIGH, AND UPPER PART OF LEG OF HORSE,
INTERNAL VIEW.

_L_, Lumbar vessels; _V.c._, posterior vena cava; _A_, aorta
(termination); _C_, sympathetic trunk; _1_, internal iliac artery,
_2_, lateral sacral artery; _3_, middle coccygeal artery; _4_,
lateral coccygeal artery; _5_, umbilical artery (cut off); _6_,
internal pudic artery; _6′_, vesico-prostatic artery; _7_, obturator
artery; _8_, a. profunda penis (from left obturator); _9_, posterior
gluteal (or ischiatic) vessels; _10_, external iliac artery; _11_,
_11′_, deep femoral artery; _12_, prepubic artery; _13_, branch of
deep femoral artery; _14_, great sciatic nerve; _15_, posterior
gluteal nerve; _16_ (above), internal pudic nerve; _16_ (below near
pelvic outlet), suburethral venous plexus; _17_, sacro-coccygeus
inferior; _18_, coccygeus; _19_, recto-coccygeus; _20_, retractor
ani; _21_, _21′_, two heads of obturator internus; _22_, symphysis
pelvis; _23_, prepubic tendon; _24_, suspensory ligament of penis;
_25_, retractor penis muscle; _26_, bulbo-cavernosus muscle; _27_,
urethra (cross-section); _28_, crus penis (cross-section); _29_,
suspensory ligaments of anus (= upper part of retractor penis
muscle); _30_, anal lymph glands; _31_, tibial nerve. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]

THE INTERNAL ILIAC ARTERY

The =internal iliac= or =hypogastric arteries= (Aa. hypogastricæ) result from the bifurcation of the aorta under the fifth or sixth lumbar vertebra. They diverge at an angle of about 60 degrees, and each passes backward under the wing of the sacrum, then inclines downward on the pelvic surface of the shaft of the ilium, and divides a little above the psoas tubercle into iliaco-femoral and obturator arteries. The chief branches are as follows:

FIG. 452.—DISSECTION OF PERINEUM OF HORSE (MALE).

_1_, Bulbo-urethral (Cowper’s) gland; _2_, transversus perinei muscle
(?); _3_, ischio-urethral muscle; _4_, retractor penis muscle; _5_,
bulbo-cavernosus muscle. (After Schmaltz, Atlas d. Anat. d.
Pferdes.)
]

1. The last pair of =lumbar arteries= pass up through the foramina at the junction of the last lumbar vertebra and the sacrum.

2. The =internal pudic artery= (A. pudenda interna) arises near the origin of the internal iliac. It passes backward and somewhat downward, at first along the iliac head of the obturator internus, then above the superior ischiatic spine on the inner surface of the sacro-sciatic ligament, perforates the latter and runs for a variable distance in its substance or on its external face. It then re-enters the pelvic cavity, passes backward on the retractor ani to the ischial arch, and divides into the perineal and the artery of the bulb in the male, perineal and artery of the clitoris in the female. It is accompanied by the internal pudic nerve. Its chief branches are as follows:

(1) The =umbilical artery= is given off from the internal pudic about an inch (ca. 2 to 3 cm.) from the origin of that vessel. It is a very large artery in the fœtus, in which it curves downward and forward at the side of the bladder in the edge of the umbilical fold of peritoneum, passes through the umbilical opening, becomes a component of the umbilical cord and ramifies in the fœtal placenta. After birth it extends only to the vertex of the bladder and is much reduced. Its lumen is almost obliterated and its wall is very thick, giving the vessel a cord-like character, hence it is commonly termed the round ligament of the bladder.[167] It gives off small =vesical branches= (Aa. vesicates craniales) to the bladder, and twigs to the prostate and vasa deferens in the male. In the mare a small branch runs forward along the ureter into the broad ligament of the uterus.

FIG. 453.—DISSECTION OF PERINEUM OF MARE.

_1_, Sacro-coccygeus superior; _2_, sacro-coccygeus lateralis; _3_,
intertransversales; _4_, sacro-coccygeus inferior; _5_,
recto-coceygeus; _6_, sphincter ani externus; _6′_, branch
connecting sphincter ani with constrictor vulvæ; _7_, vestibular
bulb; _8_, tuber ischii; _9_, sacro-sciatic ligament. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]

(2) The =middle hæmorrhoidal= or =vesico-prostatic artery= (A. hæmorrhoidalis media) in the male arises usually near the prostate and runs backward lateral to the rectum. It supplies branches to the rectum, bladder, urethra, and accessory genital glands. In the female the homologous vessel is much larger and gives off the =posterior uterine artery= (A. uterina caudalis). This runs forward on the side of the vagina, to which it gives branches, and ramifies on the body of the uterus, anastomosing with the anterior and middle uterine arteries. (In some cases this artery arises from the internal iliac or the umbilical.)

(3) The =perineal artery= (A. perinei) is relatively small in the male. It passes upward at the side of the anus, which it supplies, and gives twigs to the bulbo-cavernosus muscle and the skin of the perineum. In the female it is large and is distributed to the anus and vulva, and gives a large branch to the vestibular bulb.

(4) The =artery of the bulb= (A. bulbi urethræ) may be regarded as the direct continuation of the internal pudic in the male. It lies at the side of the urethra above the ischial arch, dips under the bulbo-cavernosus muscle, and ramifies in the corpus spongiosum. Before doing so it gives off a small branch which turns around the ischial arch to reach the dorsum penis, and anastomoses with the deep branch of the obturator.

(4_a_) The =artery of the clitoris= (A. clitoridis) is the homologue in the female of the preceding vessel, but is much smaller. It passes to the ventral surface of the vulva with the internal pudic nerve, supplies the clitoris, and gives twigs to the vulva.

FIG. 454.-CROSS-SECTION OF TAIL OF HORSE.

_1_, Dorso-lateral coccygeal vessels and nerve; _2_, ventro-lateral
coccygeal artery and nerve; _3_, middle coccygeal artery; _4_,
sacro-coccygeus superior; _4′_, sacro-coccygeus lateralis; _5_,
_5′_, intertransversales; _6_, sacro-coccygeus inferior; _7_,
recto-coccygeus; _8_, coccygeal fascia; _9_, fibro-cartilage between
fourth and fifth coccygeal vertebra. The veins are black.
]

3. The =lateral sacral artery= (A. sacralis lateralis) arises at the lumbo-sacral articulation (Fig. 451). It passes backward under the wing of the sacrum, then along the pelvic surface of the bone below the inferior sacral foramina and the nerves emerging from them, and is continued by the lateral coccygeal artery. The branches are as follows:

(1) =Spinal branches= (Rami spinales) enter the vertebral canal through the foramen between the last lumbar vertebra and the sacrum and through the ventral sacral foramina. They give off branches to the spinal cord and its membranes which reinforce the ventral spinal artery, and others which emerge through the dorsal sacral foramina and supply the muscles and skin of the croup.

(2) The =middle coccygeal artery= (A. coccygea) is an unpaired vessel which arises from the right or left lateral sacral or from a lateral coccygeal artery. It passes backward on the pelvic surface of the sacrum to the median line and continues in that position along the tail between the depressor muscles, supplying these and the skin.

FIG. 455.—DISSECTION OF PELVIS, THIGH, AND LEG OF HORSE, EXTERNAL
VIEW.

_1_, Dorsal branches of last intercostal and first three lumbar
nerves; _2_, cutaneous branch of fourth lumbar nerve; _3_, ventral
branches of last intercostal nerve: _4_, branches of
ilio-hypogastric nerve; _5_, superficial branch of ilio-inguinal
nerve; _6_, great sciatic nerve; _7_, _8_, nerves to biceps femoris
(from posterior gluteal nerve); _9_, nerve to semitendinosus (from
same); _10_, posterior cutaneous nerve of thigh; _11_, internal
pudic nerve; _12_, anterior gluteal vessels and nerves; _13_,
posterior gluteal (or ischiatic) vessels; _14_, branches of
obturator vessels; _15_, proximal muscular branches of great sciatic
nerve to biceps femoris, semitendinosus, and semimembranosus; _16_,
nerve to tensor fasciæ latæ (from anterior gluteal nerve); _17_,
gluteus profundus; _18_, stump of gluteus medius; _19_, gemellus;
_20_, trochanter major; _21_, stump of biceps femoris; _22_,
sacro-coccygeus superior; _22′_, sacro-coccygeus lateralis; _23_,
coccygeus; _24_, sacro-coccygeus inferior; _25_, line of fusion of
aponeuroses of internal and external oblique muscles of abdomen;
_25′_, aponeurosis of external oblique muscle (lamina iliaca); _26_,
branches of iliaco-femoral vessels; _27_, ilio-lumbar vessels; _28_,
ilio-lumbar ligament or deep layer of lumbo-dorsal fascia; _29_,
external angle of ilium; _30_, internal angle of ilium; _31_,
lateral sacro-iliac ligament; _32_, sacro-sciatic ligament. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]

(3) The =posterior gluteal= or =ischiatic artery= (A. glutea caudalis) emerges through the upper part of the sacro-sciatic ligament and runs backward and downward on the latter under cover of the biceps femoris (Fig. 455). It gives branches to that muscle and to the semitendinosus and semimembranosus, and anastomoses with the obturator, deep femoral, and posterior femoral arteries.

(4) The =lateral coccygeal artery= (A. caudalis lateralis ventralis) continues the direction of the lateral sacral, but is much smaller than the preceding vessel. It passes back between the depressor and intertransversales muscles of the tail and divides into two branches which supply twigs to the muscles and skin.

4. The =ilio-lumbar artery= (A. iliolumbalis) arises at a right angle from the internal iliac and runs outward behind the sacro-iliac joint, crossing the ventral surface of the ilium under cover of the iliacus muscle. It gives branches to the ilio-psoas and longissimus, and terminates by turning around the external border of the ilium a little behind the external angle, giving branches to the gluteus medius and tensor fasciæ latæ (Fig. 455).

FIG. 456.—DEEP DISSECTION OF VENTRAL WALL OF PELVIS OF HORSE (MALE).

_1_, External pudic artery and small satellite vein; _2_, anastomosis
between external pudic and internal circumflex veins; _3_, accessory
ligament; _4_, round ligament; _5_, transverse ligament; _6_, head
of femur; _7_, obturator externus (stumps); _8_, inner margin of
obturator foramen; _9_, origin of gracilis; _10_, origin of
adductor; _11_, bulbo-cavernosus; _12_, retractor penis; _13_,
suspensory ligament of penis. (After Schmaltz, Atlas d. Anat. d.
Pferdes.)
]

5. The =anterior gluteal artery= (A. glutea cranialis) is the largest branch of the internal iliac. It arises usually opposite to the preceding vessel and passes outward through the great sacro-sciatic foramen, dividing into several branches as it emerges; these enter the gluteal muscles (Fig. 455).

6. The =iliaco-femoral= or =external circumflex artery= (A. cireumflexa femoris lateralis) passes downward and outward across and beneath the shaft of the ilium, under cover of the iliacus muscle, and dips in between the rectus femoris and vastus externus. It is accompanied by two satellite veins. It gives collateral branches to the ilio-psoas, the glutei, and the tensor fasciæ latæ, supplies the nutrient artery of the ilium, and terminates in the quadriceps femoris (Fig. 455).

7. The =obturator artery= (A. obturatoria), the inner terminal branch of the internal iliac, passes downward and backward on the pelvic surface of the shaft of the ilium along the ventral border of the iliac head of the obturator internus, accompanied by the satellite vein and nerve, which lie in front of the artery (Fig. 451). On reaching the anterior border of the obturator foramen it dips under the obturator internus and passes obliquely through the foramen. In this part of its course it gives off a vesical branch and twigs to the obturator internus and the hip joint. After its emergence from the pelvic cavity it runs backward on the ventral face of the ischium, passes through the semimembranosus and, in the male, enters the crus penis, forming the arteria profunda penis. It anastomoses with the internal pudic, and usually with the external pudic by a branch which runs forward on the dorsum penis. Large collateral branches are detached to the adductors of the thigh, the biceps femoris and semitendinosus, forming anastomoses with the deep femoral and posterior femoral arteries. In the female the terminal part is small and enters the root of the clitoris.

ARTERIES OF THE PELVIC LIMB

The main arterial trunk of each pelvic limb descends as far as the lower border of the popliteus muscle, where it divides into the anterior and posterior tibial arteries. The different parts of the trunk receive special names which correspond to the several regions through which it passes. In the abdomen it is termed the =external iliac artery=, in the proximal two-thirds of the thigh it is called the =femoral artery=, while below this it is termed the =popliteal artery=.

THE EXTERNAL ILIAC ARTERY (Figs. 450, 451)

The =external iliac artery= (A. iliaca externa) arises from the aorta under the fifth lumbar vertebra, usually just in front of the origin of the internal iliac. It descends at the side of the pelvic inlet along the tendon of the psoas minor, crosses the insertion of that muscle, and reaches the level of the anterior border of the pubis, where it becomes the femoral artery. It is covered by the peritoneum and fascia, and is related behind to the corresponding vein. Its branches are as follows:

1. The =circumflex iliac artery= (A. circumflexa ilium profunda) arises from the external iliac at its origin or from the aorta directly. It passes across the iliac fascia toward the external angle of the ilium, near which it divides into two branches. The artery lies between the fascia and the peritoneum and is accompanied by two veins and the external cutaneous nerve of the thigh. The =anterior branch= gives twigs to the iliacus and psoas muscles, and passes downward and forward in the flank between the obliquus internus and transversus abdominis, in which it ramifies. The =posterior branch= perforates the abdominal wall and runs downward on the inner face of the tensor fasciæ latæ to the fold of the flank, supplying branches to that muscle, the panniculus, the precrural lymph glands, and the skin.

2. The =cremasteric artery= (A. spermatica externa) is a very small vessel which arises in a variable manner. It springs most often from the external iliac near its origin, but may come from the circumflex iliac, the aorta between the external and internal iliac, or the latter vessel. It accompanies the cremaster muscle to the inguinal canal, supplies twigs to that muscle, the tunica vaginalis, and other constituents of the spermatic cord (Fig. 450).

2_a_. The =middle uterine artery= (A. uterina media) of the female is regarded as the homologue of the preceding vessel. It has a similar origin, but is a much larger artery, which passes between the layers of the broad ligament and reaches the horn of the uterus close to its junction with the body. It is distributed to both, and anastomoses with the anterior and posterior uterine arteries.

THE FEMORAL ARTERY (Figs. 450, 451)

The =femoral artery= is the main arterial trunk of the thigh. It begins at the level of the anterior border of the pubis, from which it is separated by the femoral vein. It descends almost vertically in the femoral canal behind the sartorius muscle, covered at first by the internal femoral fascia and lower down by the gracilis. After passing over the insertion of the pectineus, it perforates the adductor muscle, crosses in the vascular groove of the posterior surface of the femur, and is continued between the two heads of the gastrocnemius as the popliteal artery. It is related at its origin to the sartorius in front, the femoral vein behind (which separates it from the pectineus), and the iliacus externally. Lower down it is related superficially to the deep inguinal lymph glands, and deeply to the vastus internus, while the saphenous nerve is in front of it, and the vein passes to its external face. The chief branches are as follows:

FIG. 457.—DISSECTION OF INGUINAL REGION AND INNER SURFACE OF THIGH OF
HORSE.

_1_, External pudic artery; _2_, anterior branches of _1_; _3_,
posterior branches of _1_; _4_, transverse anastomosis between
external pudic veins; _4′_, venous plexus of dorsum penis; _5_,
femoral artery; _6_, saphenous nerve; _7_, anterior border of
external inguinal ring; _8_, obliquus abdominis internus; _9_,
posterior border of external inguinal ring; _10_, tunica vaginalis;
_11_, vas deferens; _12_, cremaster muscle; _13_, prepuce; _14_,
glans penis; _15_, external urethral orifice; _16_, posterior
branches of circumflex iliac vessels; _17_, saphenous vessels; _18_,
fold of flank; _19_, penis (cut); _A_, superficial inguinal lymph
glands; _B_, precrural lymph glands; _C_, deep inguinal lymph
glands. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]

1. The =prepubic artery= (Truncus pudendo-epigastricus) arises from the femoral artery at its origin, usually by a common trunk with the deep femoral. It passes forward and a little inward and downward across the edge of the inguinal ligament, and then runs on the abdominal surface of the ligament to the inner part of the internal inguinal ring, where it divides over the upper border of the internal oblique muscle into the posterior abdominal and external pudic arteries.

(1) The =posterior abdominal artery= (A. epigastrica caudalis) passes along the external border of the rectus abdominis and anastomoses in the umbilical region with the anterior abdominal artery (Figs. 272). It supplies branches to the rectus and obliquus internus muscles.

(2) The =external pudic artery= (A. pudenda externa) descends on the inguinal ligament through the inner part of the inguinal canal and emerges at the inner angle of the external ring. In the male it divides into the =subcutaneous abdominal artery= and the =dorsal artery of the penis=. The former runs forward a short distance from the linea alba, and gives branches to the superficial inguinal lymph glands, the sheath, and the scrotum. The latter passes to the dorsum penis and ends at the glans as the arteria glandis. It gives off collateral branches (Rami profundi penis) to the corpus cavernosum, one of which usually passes backward and anastomoses with a branch of the obturator artery. Branches are also supplied to the superficial inguinal lymph glands, the prepuce, and the scrotum. In the female the =mammary artery= takes the place of the dorsal artery of the penis; it plunges into the base of the mammary gland.

2. The =deep femoral artery= (A. profunda femoris) arises either by a common trunk with the prepubic or a little distal to it (Fig. 451). It passes backward and downward across the inner face of the femoral vein, then below the pubis in the space between the hip joint and the pectineus muscle. On reaching the obturator externus it inclines more ventrally and outward, passes out between the internal border of the femur and the quadratus femoris, and ramifies in the biceps femoris and semitendinosus. It supplies large collateral branches to the adductor muscles and twigs to the deep inguinal lymph glands and the hip joint.

3. The =anterior femoral artery= (A. femoralis cranialis) arises a little distal to the preceding vessel from the opposite side of the femoral trunk. It passes forward, outward, and a little downward across the deep face of the sartorius, and dips in between the rectus femoris and vastus internus (Fig. 451). It is related externally to the ilio-psoas and the femoral nerve.

In some cases this artery is replaced by a large branch of the
external circumflex, which passes between the ilio-psoas and rectus
femoris and enters the interstice between the latter muscle and the
vastus internus.

4. Innominate =muscular branches= (Rami musculares) of variable size and arrangement are given off to the muscles of this vicinity.

5. The =saphenous artery= (A. saphena) is a small vessel which arises from the femoral about its middle or from a muscular branch, and emerges between the sartorius and gracilis or through the latter to the inner surface of the thigh (Fig. 457). It is joined by the large saphenous vein and the saphenous nerve and passes down superficially on the fore part of the gracilis, continues on the deep fascia of the leg, and divides above the hock into two branches, which accompany the radicles of the vein. It gives off cutaneous twigs and anastomoses with the recurrent tibial artery.

In some cases this anastomosis does not occur. The artery may be
larger and directly continuous with the internal tarsal artery.

6. The =articular branch= (A. genu suprema) is a slender artery which arises from the femoral just before it passes through the adductor. It descends along the posterior border of the vastus internus to the inner surface of the stifle joint, where it ramifies.

7. The =nutrient artery of the femur= (A. nutritia femoris) is given off at the middle of the femur and enters the nutrient foramen.

8. The =posterior femoral= or =femoro-popliteal artery= (A. femoris caudalis) is a large vessel which arises from the posterior face of the femoral just before the trunk passes between the two heads of the gastrocnemius (Fig. 455). It is very short and divides into two branches. The ascending branch passes upward and outward between the adductor (in front) and the semimembranosus (behind), and enters the biceps femoris, in which it ramifies. The descending branch passes downward and backward on the external head of the gastrocnemius, then curves upward between the biceps femoris and semitendinosus (crossed externally by the tibial nerve) and divides into branches to these muscles. A branch is detached from the convexity of the curve which passes down between the heads of the gastrocnemius, gives branches to that muscle and the flexor perforans, and is continued by a slender artery which accompanies the tibial nerve and unites with the recurrent tibial artery. A branch ascends alongside of the sciatic nerve between the biceps and semitendinosus and anastomoses with a descending branch of the obturator.

THE POPLITEAL ARTERY

This artery (A. poplitea) is the direct continuation of the femoral. It lies between the two heads of the gastrocnemius, at first on the posterior face of the femur, then on the femoro-tibial joint capsule. It then passes down through the popliteal notch under cover of the popliteus, inclines outward, and divides near the upper part of the interosseous space into anterior and posterior tibial arteries. The satellite vein lies along its inner side. Collateral branches are supplied to the stifle joint and the gastrocnemius and popliteus.

POSTERIOR TIBIAL ARTERY

The =posterior tibial artery= (A. tibialis posterior) is much the smaller of the two terminals of the popliteal. It lies at first between the tibia and the popliteus, then between that muscle and the deep and inner heads of the deep flexor. Lower down it descends along the tendon of the inner head, becomes superficial in the distal third of the leg, and passes behind the tendon. At the level of the tuber calcis it forms an ᔕ-shaped curve, runs downward along the deep flexor tendon accompanied by the plantar nerves, and divides at the lower part of the hock into internal and external plantar arteries. The collateral branches are as follows:

1. The =nutrient artery of the tibia= (A. nutritia tibiæ).

2. =Muscular branches= (Rami musculares) to the popliteus and deep flexor.

3. The =external tarsal artery= (A. tarsea lateralis) arises at the distal end of the leg and is distributed to the outer surface of the hock. It gives off a small recurrent branch which ascends along the external border of the gastrocnemius tendon and anastomoses with a branch of the posterior femoral artery.

4. The =recurrent tibial artery= (A. tibialis recurrens) is given off from the second part of the curve, ascends in relation to the tibial nerve, and anastomoses with the descending branch of the posterior femoral and with the saphenous artery.

5. Small branches (internal calcaneal) to the inner aspect of the hock.

6. The =plantar arteries=, internal and external (A. plantaris medialis, lateralis), are the small terminals of the posterior tibial. They descend along the sides of the tarsal sheath of the deep flexor with the plantar nerves to the proximal part of the metatarsus, where they unite with the perforating tarsal artery to form the =plantar arch= (Arcus plantaris). Four =plantar metatarsal arteries= proceed from this arch. The two slender =superficial plantar metatarsal arteries= (A. metatarsea plantaris superficialis medialis, lateralis) descend on either side of the deep flexor tendon with the plantar nerves and unite with the great metatarsal or with the corresponding digital artery. The two =deep= or =interosseous plantar metatarsal arteries= (A. metatarsea plantaris profundus medialis, lateralis) descend between the suspensory ligament and the corresponding small metatarsal bone and unite near the fetlock with the great metatarsal. The inner artery is the larger of the two and usually appears to be the continuation of the perforating tarsal. It supplies the nutrient artery of the large metatarsal bone. In other cases it is the direct continuation of the internal plantar artery, the external artery only uniting with the perforating tarsal.

FIG. 458.—DISSECTION OF LEG AND HOCK OF HORSE, INNER VIEW. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]

ANTERIOR TIBIAL ARTERY

FIG. 459.—DEEP DISSECTION OF RIGHT STIFLE, LEG, AND HOCK OF HORSE,
POSTERIOR VIEW.

The hock is flexed at a right angle, and the tuber calcis is sawn off.
The tibial nerve is drawn inward to show its muscular branches.
Branches of tibial nerve: _1_, _2_, to gastrocnemius; _3_, _4_, to
superficial flexor; _5_, to popliteus; _6_, to flexor longus or
accessorius; _7_, to deep flexor. (After Schmaltz, Atlas d. Anat. d.
Pferdes.)
]

FIG. 460.—SUPERFICIAL DISSECTION OF RIGHT STIFLE, LEG, AND HOCK OF
HORSE, FRONT VIEW. (After Schmaltz, Atlas d. Anat. d. Pferdes.)
]

The =anterior tibial artery= (A. tibialis anterior) is much the larger of the two terminal branches of the popliteal. It passes forward through the upper part of the interosseous space and descends with two satellite veins on the outer part, of the front of the tibia, under cover of the tibialis anterior. At the lower part of the leg it deviates to the outer border of the tendon of this muscle, passes on to the capsule of the hock joint, gives off the perforating tarsal artery, and is continued asthe great metatarsal artery. It gives off =muscular branches= to the dorso-lateral group of muscles of the leg and =articular branches= to the hock. The =peroneal= branch (A. peronea) is a variable vessel which descends along the fibula under the lateral extensor; it gives off muscular branches and one which perforates the fascia and divides into ascending and descending cutaneous twigs.

The =perforating tarsal artery= (A. tarsea perforans) is given off under cover of the outer tendon of the peroneus tertius. It passes backward through the vascular canal of the tarsus with a satellite vein and unites on the upper part of the suspensory ligament with the plantar arteries (or only with the external plantar) to form the plantar arch.

In well-injected specimens it is seen that there is a fine arterial network (Rete tarsi dorsale) on the flexor surface of the hock, which is formed by twigs from the anterior tibial and lateral tarsal arteries. From it proceed two very slender =dorsal metatarsal arteries=. The inner one descends in the furrow between the inner small and large metatarsal bones, and anastomoses usually in the proximal part of the metatarsus with the internal superficial plantar metatarsal, uniting sometimes with the deep plantar metatarsal. The external vessel passes down under the periosteum on the anterior face of the large metatarsal bone and becomes lost or joins the large metatarsal artery.

Sometimes the anterior tibial artery passes undivided through the
tarsus, gives off the internal deep plantar metatarsal, and is
continued as a very large internal superficial plantar metatarsal
along the deep flexor tendon, thus resembling the arrangement in the
fore limb.

In a few cases the perforating tarsal is a large vessel, directly
continuing the anterior tibial, and is continued by a large internal
deep plantar metatarsal. The great metatarsal is then small. Other
variations are common.

THE GREAT METATARSAL ARTERY

This artery (A. metatarsea dorsalis lateralis) is the direct continuation of the anterior tibial. It passes downward and outward under the extensor brevis and the tendon of the lateral extensor, at first on the joint capsule and then in the oblique vascular groove on the upper part of the large metatarsal bone. It then descends in the groove formed by the apposition of the large and external small metatarsals, inclines inward between the two, and divides on the lower part of the posterior face of the large metatarsal bone into the internal and external digital arteries. It is not usually accompanied by a vein. Beyond this the arterial arrangement is the same as in the thoracic limb.

THE VEINS[168]

PULMONARY VEINS

The terminal =pulmonary veins= (Vv. pulmonales), usually seven or eight in number, return the aërated blood from the lungs and open into the left atrium of the heart. They are destitute of valves. Their tributaries arise in the capillary plexuses in the lobules of the lungs, and unite to form larger and larger trunks which accompany the branches of the bronchi and pulmonary arteries. A very large vein is formed by the union at an acute angle of a trunk from each lung, where the latter are adherent to each other.

SYSTEMIC VEINS

THE VEINS OF THE HEART (Figs. 426, 427)

The =coronary sinus= (Sinus coronarius) is a very short bulbous trunk which receives most of the blood from the wall of the heart. It is situated just below the termination of the posterior vena cava and is covered in part by a thin layer of ventricular muscle-fibers. It opens into the right atrium just below the posterior vena cava. It is formed by the union of two tributaries. The =great cardiac= or =left coronary vein= (V. cordis magna) begins at the left side of the apex of the heart, ascends in the left longitudinal groove and turns backward in the coronary groove, in which it winds around the posterior border of the heart to the right side and joins the coronary sinus. The =middle cardiac= or =right coronary vein= (V. cordis media) begins on the right side of the apex, ascends in the right longitudinal groove and joins the coronary sinus, or opens separately into the atrium just in front of the orifice of the left vein, so that a common trunk (coronary sinus) does not then exist.

The =small cardiac veins= (Vv. cordis minores), three to five in number, are small vessels which return some blood from the right ventricle and atrium; they open into the latter near the coronary groove in spaces between the musculi pectinati.

THE ANTERIOR VENA CAVA (Fig. 429)

The =anterior vena cava= (V. cava cranialis) returns to the heart the blood from the head, neck, thoracic limbs, and the greater part of the thoracic wall. It is formed at the ventral part of the thoracic inlet by the confluence of the two jugular and two brachial veins. Its origin is attached to the first pair of ribs. It passes backward in the anterior mediastinum, at first median and ventral to the common carotid trunk, then deviates to the right of the anterior aorta, and opens into the right atrium opposite to the third rib. The demarcation between vein and atrium is not very distinct. It contains no valves except at the mouths of its radicles. Its length is about five to six inches (ca. 12 to 15 cm.) and its caliber about two inches (ca. 5 cm.) in a subject of medium size. Its right face is crossed by the right phrenic nerve, and on the left it is related to the anterior aorta and brachiocephalic artery. It receives, in addition to small pericardial and mediastinal veins, the following tributaries:

1. The =internal thoracic vein= (V. thoracica interna) is a satellite of the artery of that name. It opens into the anterior vena cava at the first rib.

2. The =vertebral vein= (V. vertebralis) corresponds to the homonymous artery. On the right side it terminates either in front of the deep cervical vein or by a short common trunk with it. On the left side it almost always unites with the deep cervical and vertebral vein to form a common trunk.

3. The =deep= or =superior cervical vein= (V. cervicalis profunda) corresponds to the artery. On the right side it leaves the artery at the first intercostal space, crosses the right face of the trachea and opens into the vena cava; it may form a common trunk with the dorsal or vertebral. On the left side there is nearly always a common trunk for all three.

4. The =dorsal vein= (V. costo-cervicalis) corresponds to the artery. On the right side it leaves the artery on entering the thorax, crosses the right face of the trachea, and opens into the vena cava in front of the deep cervical or by a common trunk with it. On the left side it almost always joins the deep cervical and vertebral to form a short common trunk which crosses the left face of the intrathoracic part of the brachial artery opposite the second rib and opens into the anterior vena cava.

THE VENA AZYGOS

The =vena azygos= (Fig. 429) is an unpaired vessel which arises at the level of the first lumbar vertebra by radicles coming from the psoas and the crura of the diaphragm; it is connected with the first lumbar vein. It passes forward along the right side of the bodies of the thoracic vertebræ, in contact usually with the thoracic duct, which separates the vein from the aorta. At the seventh vertebra it leaves the spine, curves downward and forward over the right side of the thoracic duct, trachea, and œsophagus, and opens into the right atrium opposite the third intercostal space. Its tributaries are:

1. The last fourteen =intercostal veins= (Vv. intercostales) of the right side. On the left side the last four to seven intercostal veins usually empty into the =vena hemiazygos=. This vessel runs on the left side of the aorta from the fourteenth to the eleventh thoracic vertebra, passes between the aorta and the spine, and joins the vena azygos. In its absence its tributaries join the vena azygos.

2. The =œsophageal vein= (V. œsophagea), satellite of the œsophageal artery, joins the vena azygos as it inclines downward.

3. The =bronchial vein= (Vena bronchialis) unites with the preceding to form a short common trunk (Ellenberger-Baum), or empties into the great coronary vein (Chauveau).[169]

VEINS OF THE HEAD AND NECK

JUGULAR VEINS

The =jugular veins= (Vv. jugulares), right and left (Fig. 431), arise behind the posterior border of the lower jaw about two and a half inches (ca. 6 to 7 cm.) below the temporo-maxillary articulation by the union of the superficial temporal and internal maxillary veins. Each passes downward and backward, at first embedded more or less in the parotid gland, and continues in the jugular furrow to the thoracic inlet, where it unites with its fellow and the two brachial veins to form the anterior vena cava. In the neck it is covered by the skin, fascia, and panniculus, and is superficial to the carotid artery, from which it is separated in the anterior two-thirds of the region by the omo-hyoideus muscle.[170] It contains valves at the mouths of its tributaries and has several pairs of semilunar valves variably disposed along its course. Its tributaries are as follows:

1. The =internal maxillary vein= (V. maxillaris interna) is larger than the external maxillary. It may be considered to begin as the continuation backward of the buccinator vein where the vessel crosses the alveolar border of the mandible (about two inches (ca. 5 cm.) behind the last molar tooth). It runs backward on the inner surface of the ramus below the external pterygoid and covered by the internal pterygoid muscle for a distance of about three inches (ca. 7 to 8 cm.), then inclines a little downward and runs ventral to the artery for about an inch (ca. 2 to 3 cm.). It crosses the external face of the artery at the posterior border of the jaw, and is joined by the superficial temporal vein to form the jugular. Its principal radicles are:

(1) The =dorsal lingual vein= (V. dorsalis linguæ), which is a satellite of the lingual nerve.

(2) The =inferior alveolar= or =dental vein= (V. alveolaris mandibulæ), a satellite of the corresponding artery. It often unites with the preceding.

(3) =Pterygoid veins= (Rami pterygoidei).

(4) The =deep temporal vein= (V. temporalis profunda) is a large vessel which receives tributaries from the temporalis muscle and emissaries from the parieto-temporal canal. It is connected with the anterior cerebral vein and usually with the meningeal veins by its frontal branch. The latter drains chiefly the lacrimal gland and passes behind the supraorbital process.

2. The =superficial temporal vein= (V. temporalis superficialis) is a satellite of the corresponding artery. It is formed by the confluence of the =anterior auricular= and =transverse facial veins=. The former receives the =superior cerebral vein= (V. cerebralis dorsalis), which is the emissary of the transverse sinus of the dura mater; it emerges from the parieto-temporal canal behind the postglenoid process. The =transverse facial vein= (V. transversa faciei) runs at first above the artery of like name, then plunges deeply into the masseter and unites in front with the facial vein. It is connected with the vena reflexa.

3. The =inferior masseteric= or =maxillo-muscular vein= (V. masseterica) joins the jugular at the upper border of the sterno-cephalicus tendon. It is a short trunk formed by the confluence at the posterior border of the jaw of masseteric and pterygoid veins. The former is usually connected by a large branch with the buccinator vein.

FIG. 461.—SUPERFICIAL VESSELS AND NERVES OF HEAD AND ANTERIOR PART OF
NECK OF HORSE.

_a_, Masseter; _b_, parotid gland; _c_, parotido-auricularis; _1_,
masseteric artery; _2_, parotid branch; _3_, transverse facial
artery; _4_, facial artery; _5_, _6_, inferior labial artery; _7_,
superior labial artery; _8_, lateral nasal artery; _9_, infraorbital
artery; _10_, dorsal nasal artery; _11_, angular artery of eye;
_12_, _13_, jugular vein; _14_, great auricular vein; _15_,
masseteric vein; _16_, superficial temporal vein; _17_, transverse
facial vein; _17′_, deep temporal vein; _18_, external maxillary
vein; _19_, facial vein; _20_, labial vein; _21_, dorsal nasal vein;
_22_, lateral nasal vein; _23_, angular vein of eye; _24_, _25_,
facial nerve; _25′_, _25″_, superior and inferior buccal nerves;
_26_, transverse facial nerve; _27_, auriculo-palpebral nerve; _28_,
anterior auricular nerve; _29_, cervical branch of facial nerve;
_30_, ventral branch of second cervical nerve; _30′_, _30″_, _30‴_,
auricular and cutaneous branches of _30_; _31_, branches of dorsal
division of first and second cervical nerves; _32_, dorsal branch of
spinal accessory nerve. (After Leisering’s Atlas.)
]

4. The =great auricular vein= (V. auricularis magna) is a satellite of the posterior auricular artery above, but joins the jugular a variable distance below and behind the point of origin of the artery.

5. The =inferior cerebral vein= (V. cerebralis ventralis) is an emissary of the cavernous sinus of the dura. It is a satellite of the internal carotid artery, receives the =condyloid vein=, and joins the jugular near the occipital vein or by a common trunk with it.

6. The =occipital vein= (V. occipitalis) arises in the fossa atlantis by the union of muscular and cerebrospinal branches. The former comes from the muscles of the poll and passes through the foramen transversarium. The latter is connected with the occipital sinus of the dura mater and emerges from the spinal canal by the intervertebral foramen.