Chapter V: Muscles of the Leg and Foot (10)

The removal of the other abdominal viscera has allowed the ovaries and
uterus to sink down, whereas they are normally in contact with the
roof of the cavity in the non-pregnant subject. _1_, Left ovary;
_2_, Fallopian tube; _3_, left cornu uteri; _4_, right cornu uteri;
_5_, corpus uteri; _5′_, portio vaginalis uteri, and _5″_, os uteri,
seen through window cut in vagina; _6_, broad ligament of uterus;
_6″_, round ligament; _7_, vagina; _8_, labia vulvæ; _9_, rima
vulvæ; _9′_ superior commissure, and _9′_, inferior commissure of
vulva; _10_, constrictor vulvæ; _11_, position of vestibular bulb;
_12_, ventral wall of abdomen; _13_, left kidney; _14_, left ureter;
_15_, urinary bladder; _16_, urethra; _17_, rectum; _18_, anus;
_19_, _19′_, unpaired and paired parts of sphincter ani externus;
_20_, retractor ani cut at disappearance under sphincter; _21_,
suspensory ligament of anus; _22_, longitudinal muscular layer of
rectum; _22′_, recto-coccygeus; _23_, constrictor vaginæ; _a_,
utero-ovarian artery, with ovarian (_a′_) and uterine (_a″_)
branches; _b_, uterine artery; _c_, umbilical artery; _d_, ischium;
_e_, pubis; _f_, ilium. (After Ellenberger, in Leisering’s Atlas.)
]

The =ovaries= (Ovaria) of the mare are bean-shaped, and are much smaller than the testicles. Their size varies much in different subjects, and they are normally larger in young than in old animals; one ovary is often larger than the other. They are about three inches (ca. 7 to 8 cm.) long and an inch to an inch and a half (ca. 3 to 4 cm.) thick. The weight is about two and a half to three ounces (ca. 70 to 80 grams).

Each presents for description two surfaces, two borders, and two extremities or poles. The =surfaces= are termed internal and external (Facies medialis, lateralis); they are both smooth and rounded.[149] The =attached= or =mesovarial border= (Margo mesovaricus) is convex. It is inclosed in a part of the broad ligament termed the mesovarium; the vessels and nerves reach the gland at this border. The =free border= (Margo liber) is marked by a notch which leads into a depression, the =ovulation fossa=. The =tubal= or =anterior extremity= (Extremitas tubaria) is rounded, and is related to the fimbriated end of the uterine or Fallopian tube. The =uterine= or =posterior extremity= (Extremitas uterina) is also round, and is connected with the horn of the uterus by the ovarian ligament.

The ovaries are situated in the sublumbar region of the abdominal cavity, about a handbreadth behind the corresponding kidney. They are in contact with the lumbar wall of the abdomen, and are commonly about two or three inches (ca. 5 to 7.5 cm.) from the median plane. The distance from the ovaries to the vulvar orifice is about twenty inches (ca. 50 cm.) in a mare of medium size. The attached (mesovarial) border is commonly directed toward the median plane, the free border laterally and somewhat ventrally.

The position of the ovaries is not constant, but is subject to less
variation than might be expected from their mode of attachment. The
normal variations in the non-pregnant state are chiefly in a
transverse direction, and do not usually exceed two or three inches
(ca. 5 to 7 cm.). It is not at all rare to find the ovary deflected
medially, so that the external surface faces ventrally. In the
longitudinal direction little variation appears to occur. The right
ovary is usually about four or five inches (ca. 10 to 12 cm.), and the
left one about three or four inches (ca. 8 to 10 cm.), behind the
corresponding kidney. Thus they lie about in a transverse plane
tangent to the external angles of the ilia, i. e., through the fifth
lumbar vertebra. They may be about two inches (ca. 5 cm.) from the
extremity of the corresponding cornu of the uterus or in contact with
it. The right ovary commonly lies a little (ca. 2.5 cm.) further
forward than the left one. Except during pregnancy, they are normally
in contact with the lumbar abdominal wall, and do not hang down among
the adjacent viscera.

FIG. 408.—RIGHT OVARY OF MARE, WITH ADJACENT STRUCTURES.

The extremity of the cornu uteri is opened. _1_, Ovary; _2_, Fallopian
tube, with its ostium abdominale (_2′_), fimbriæ (_2″_), and ostium
uterinum (_2‴_); _3_, cornu uteri, with its mucous lining (_3′_);
_4_, ovarian ligament; _4′_, mesosalpinx. (After Ellenberger, in
Leisering’s Atlas, reduced.)
]

The ovary is attached to the sublumbar region by the anterior part of the broad ligament; this part of the ligament, the =mesovarium=, is about three or four inches (ca. 8 to 10 cm.) wide, measured from the ovary directly to the parietal attachment. The uterine or posterior extremity of the ovary, is connected with the extremity of the cornu of the uterus by the =ovarian ligament= (Ligamentum ovarii proprium); this is a band of unstriped muscle inclosed between the layers of the broad ligament.

=Structure.=—The greater part of the surface of the ovary has a covering of peritoneum. The peritoneal investment is absent at the attached border where the vessels and nerves enter; this area is termed the =hilus=. The ovulation fossa is covered by a layer of columnar cells, a remnant of the primitive =germinal epithelium=. The =stroma= of the ovary (Stroma ovarii) is a network of connective tissue and unstriped muscular fibers. In the deeper or medullary portion of the stroma (Zona vasculosa) the meshes are largely occupied by the numerous blood-vessels. In the peripheral or cortical portion (Zona parenchymatosa) are numerous =ova= (Ovula) in various stages of development. The immature ova are surrounded by follicle cells; those more advanced in development are inclosed also by a condensation of the stroma termed the =theca folliculi=; within the theca is a quantity of fluid, the =liquor folliculi=. These constitute the =Graafian follicles= (Folliculi oöphori), which enlarge as they mature, becoming visible to the naked eye as vesicles with a diameter of a centimeter or more. When fully developed, the follicles are superficially situated, and often project slightly from the surface of the ovary. At intervals follicles rupture and their contents escape. This process, which sets free the ovum, is termed =ovulation=; it takes place in the mare only at the ovulation fossa, and occurs during the periods of œstrum.

FIG. 409.—SCHEMATIC REPRESENTATION OF CHANGES IN OVARY OF MARE FROM
FŒTAL TO ADULT STATE. (After Born.)

The changes affect chiefly the free border (upper in figure) and the
extent and form of the area covered by germinal epithelium (_4_).
_1_, Peritoneum (broad ligament); _2_, ligament of ovary; _3_,
fimbria of Fallopian tube; _4_, germinal epithelium; _5_, vessels,
which reach the ovary at the attached border (_6_). The latter
represents the hilus, while the deep depression at the free border
is the ovulation fossa. (Ellenberger, in Leisering’s Atlas.)
]

After rupture of a follicle its cavity is partly occupied by a
blood-clot, constituting what may be termed a =corpus rubrum=. By
proliferation and enlargement and fatty changes, the follicle cells
are transformed into lutein cells, forming a yellow mass known as a
=corpus luteum=. If impregnation takes place, the accompanying
increase in vascularity of the organs may cause the corpus luteum to
reach a large size; if impregnation does not occur, it is much
smaller, and is sooner replaced by scar tissue, the =corpus albicans=.

In the young foal the ovaries are large and oval in form. The free
border is convex and is covered by germinal epithelium, which extends
over part of the surfaces also. This area is distinguishable by its
dull gray appearance from the peritoneal surface, which has the usual
smooth glistening character. As growth proceeds the ovary gradually
becomes bent until it assumes its definitive curved shape. The
germinal epithelium is then limited to the ovulation fossa. The ovary
migrates somewhat during development from its primitive position,
which is the same as that of the testicle.

In old animals the ovaries commonly consist largely of fibrous tissue, in which there are often cysts of various sizes. The ova, present in enormous number at birth, have then been extruded, or destroyed by phagocytic action or degeneration.

=Vessels and Nerves.=—The =arteries= of the ovary are derived from the =ovarian artery=. The artery is relatively large and is flexuous; it reaches the attached border of the ovary by passing between the layers of the mesovarium. The veins are large and numerous. They form a plexus somewhat like that of the spermatic cord. The =lymph vessels= pass to the lumbar glands. The =nerves= are derived from the sympathetic system through the renal and aortic plexuses. They accompany the arterial branches.

THE UTERINE OR FALLOPIAN TUBES

The =uterine= or =Fallopian tubes= (Tubæ uterinæ) act as excretory ducts of the ovaries, since they convey the ova from the reproductive glands to the uterus. They are not, however, in direct continuity with the glands, but rather partly in contiguity with, and partly attached to, them.[150] They are two flexuous tubes, about ten to twelve inches (ca. 25 to 30 cm.) long, which extend from the extremities of the uterine cornua to the ovaries. Each is inclosed in a peritoneal fold, derived from the external layer of the broad ligament, and termed the =mesosalpinx=. This largely covers the outer aspect of the ovary, and forms with it and the broad ligament a pouch called the =bursa ovarica=. The =uterine extremity= of the tube communicates with the cavity of the cornu by a minute orifice, the =ostium uterinum=. The =ovarian= or =fimbriated extremity= is expanded into a funnel-shaped =infundibulum=. The margin of the latter is slit into irregular processes or =fimbriæ=, some of which, the =fimbriæ ovaricæ=, are attached in the ovulation fossa. In the center of the fimbriated extremity is a small opening, the =ostium abdominale=, by which the tube communicates with the peritoneal cavity. The tube appears normally to be applied to the ovary, so that the extruded ova pass into it and are conveyed to the uterus.[151]

Pedunculated cysts, the hydatids of =Morgagni=, are often found on one
or more of the fimbriæ. In the mesosalpinx are blind flexuous tubules,
which constitute the =paroöphoron=, a remnant of the Wolffian body.
They are most evident in the young adult, and tend to disappear with
increasing age. Not uncommonly they give rise to cysts.

=Structure.=—The tube is covered externally by a =serous coat= formed by the mesosalpinx. The serous membrane is continued on the fimbriæ, and meets the mucous lining on them. The =fibrous coat= or adventitia is continuous with the fibrous lamina of the broad ligament. The =muscular coat= consists chiefly of circular fibers, although longitudinal fibers occur externally. The =mucous coat= is thin and is much plicated. The folds (Plicæ tubariæ) are chiefly longitudinal, but in the wide part of the tube (Ampullæ tubæ) they are very complex, so that on cross-sections the spaces between the folds may be mistaken for branched tubular glands. The folds are continued on to the fimbriæ. The =epithelium= is a single layer of columnar ciliated cells, the cilia producing a current directed toward the uterus. At the fimbriated extremity this epithelium passes gradually into the squamous type of the serous coat.

=Vessels and Nerves.=—The =arteries= are derived from the =utero-ovarian artery=. The =veins= are satellites of the arteries. The =lymphatics= pass with the ovarian vessels to the lumbar glands. The nerves have a similar origin to those of the ovary.

THE UTERUS

The =uterus= is a hollow muscular organ, which receives the Fallopian tubes anteriorly and opens into the vagina posteriorly. It is situated chiefly in the abdominal cavity, but extends a short distance into the pelvic cavity. It is attached to the lumbar wall of the abdomen and the lateral walls of the pelvic cavity by two folds of peritoneum termed the broad ligaments. It consists of two cornua or horns, the body, and the neck.

The =cornua= or =horns= of the uterus (Cornua uteri) are situated entirely in the abdomen. They appear to vary considerably in position; commonly they are pressed up against the sublumbar muscles by the intestine (left portions of large colon, small colon, and small intestine). They are cylindrical, and are about ten inches (ca. 25 cm.) in length. The anterior extremity of each forms a blunt point which receives the Fallopian tube. Posteriorly they increase somewhat in caliber, converge, and unite with the body. The =dorsal= (or attached) =border= is slightly concave and is attached to the broad ligament. The =ventral border= is convex and free.

FIG. 410.—GENITAL ORGANS OF MARE, DORSAL VIEW.

The left cornu and adjacent part of the body of the uterus and the
vagina and vulva are opened up. _1_, Ovary; _2_, Fallopian tube,
with _2′_, its fimbriated end; _3_, cavity of corpus uteri; _4_,
cavity of left cornu; _5_, right cornu, with _5′_, its communication
with the body; _6_, portio vaginalis uteri; _6′_, os uteri; _7_,
broad ligament of uterus; _8_, ligament of ovary; _9_, vagina; _10_,
vulva; _10′_, glandulæ vestibulares majores; _10″_, glandulæ
vestibulares minores; _11_, transverse fold; _12_, external urethral
opening; _13_, _13′_, labia vulvæ; _14_, glans clitoridis; _14′_,
junction of crura to form corpus clitoridis indicated by dotted
lines; _15_, urinary bladder; _a_, utero-ovarian artery with ovarian
(_a′_) and uterine (_a″_) branches; _b_, uterine artery. (After
Ellenberger, in Leisering’s Atlas.)
]

When a soft uterus is distended, the cornua are strongly curved, but
this does not represent the natural form. When fixed _in situ_ the
horns are either slightly curved or nearly straight. The two horns are
commonly unsymmetrical in length and diameter in mares which have
borne young.

The =body= of the uterus (Corpus uteri) is situated partly in the abdomen, partly in the pelvic cavity. It is cylindrical, but considerably flattened dorso-ventrally, so that in cross-section it is elliptical. Its average length is about six inches (15 cm.), and its diameter, when moderately distended, about four inches (10 cm.). Its =dorsal surface= (Facies rectalis) is related to the small colon and rectum. Its =ventral surface= (Facies vesicalis) is in contact with the bladder, and has inconstant relations with various parts of the intestine. The term =fundus uteri= is applied to the anterior wide part from which the cornua diverge.

The position of the body of the uterus is variable, especially in
regard to its anterior part. It is often pressed up against the
rectum, and may be deflected to either side—most frequently to the
left—by the pelvic flexure of the colon or coils of the small colon.

The =cervix= or =neck= of the uterus (Cervix uteri) is the constricted posterior part which joins the vagina. Part of it (Portio vaginalis uteri) projects into the cavity of the vagina; it is therefore not visible externally, but may be felt through the vaginal wall. It is about two inches (5 cm.) in length, and an inch and a half (3.5 to 4 cm.) in diameter.

=Attachments.=—The body and cornua are attached to the abdominal and pelvic walls by two extensive peritoneal folds, the =broad ligaments= (Ligamenta lata). These extend on either side from the sublumbar region and the lateral pelvic walls to the dorsal border of the cornua and the lateral margins of the body of the uterus. They contain the vessels and nerves of the uterus and ovaries, connective tissue, and unstriped muscular fibers. The ureters are situated along their parietal margins. The outer layer of each forms a fold, the =round ligament= of the uterus (Ligamentum teres uteri), which blends with the parietal peritoneum over the internal inguinal ring; its anterior extremity is situated above the extremity of the cornu and is rounded and free. It contains muscular tissue, vessels, and nerves, and is the homologue of the gubernaculum testis. The anterior part of the neck is continuous with the vagina, and thus has a more fixed position than the rest of the organ.

=The cavity= of the uterus (Cavum uteri) is largely obliterated in the non-pregnant state by the contraction of the wall and by folds of the mucous lining. At the extremity of each cornu it communicates by a minute opening with the Fallopian tube. The cavity of the neck is termed the =cervical canal= (Canalis cervicis); it is closed ordinarily by mucous folds and a plug of mucus. It opens into the vagina by the =os uteri externum=, and into the body by the =os uteri internum=.

=Structure.=—The wall of the uterus consists of three coats—an external serous, a middle muscular, and an internal mucous. The =serous coat= (Perimetrium) is, for the most part, closely adherent to the muscular coat. It is continuous with the broad ligaments. The =muscular coat= consists essentially of two layers, a thin external stratum of longitudinal fibers, and a thick layer of circular fibers. Between these is a very vascular layer (Stratum vasculare) of connective tissue with circular and oblique muscular fibers in it. The circular coat is very thick in the neck, where it forms a =sphincter= half an inch or more (ca. 1.5 cm.) in thickness. The =mucous membrane= rests directly on the muscular coat. It is thick, and is covered by columnar epithelium. It contains numerous long tubular =uterine glands= (Glandulæ uterinæ). It is brownish-red in color, except in the neck, where it is pale.

=Vessels and Nerves.=—The chief =arteries= are the =uterine= and the =uterine branch= of the =utero-ovarian=, which have a flexuous course in the broad ligaments; there is also a branch from the =internal pudic= artery. The =veins= form pampiniform plexuses and accompany the arteries. The =lymphatics= are numerous and go to the internal iliac and lumbar glands. The =nerves= are derived from the sympathetic through the uterine and pelvic plexuses.

The foregoing statements refer to the non-gravid uterus. In the
pregnant state it undergoes important changes in size, position, and
structure. The increase in size affects chiefly the gravid cornu
(except in the case of twins) and the body. The cornu attains a length
of about two and a half to three feet (ca. 80 to 90 cm.), and a
corresponding diameter; in this process it extends much beyond the
ovary, and the broad ligament. The gravid uterus is entirely abdominal
in position, and extends along the ventral wall, chiefly to the left
of the median plane. It weighs about nine pounds (ca. 4 kg.),
according to Ellenberger. The broad ligaments increase greatly in size
and contain more muscular tissue. The vessels are greatly enlarged and
form new branches. The muscular coat, in spite of the increase in size
and number of the fibers, is somewhat thinner, except in the neck. The
mucous membrane is thicker and more vascular; the epithelium becomes
non-ciliated and stratified.

THE VAGINA

The =vagina= is the passage which extends horizontally through the pelvic cavity from the neck of the uterus to the vulva. It is tubular, is about six to eight inches (ca. 15 to 20 cm.) in length, and, when slightly distended, about four or five inches (ca. 10 to 12 cm.) in diameter. Its dilatability appears to be limited only by the pelvic wall. There is no external line of demarcation between the vagina and the uterus or the vulva.

It is related dorsally to the rectum, ventrally to the bladder and urethra, and laterally to the pelvic wall. The recto-genital pouch of the peritoneum extends between the vagina and rectum for a distance of about two inches (5 cm.), and ventrally the vesico-genital pouch passes backward somewhat less between the vagina and bladder. Thus most of the vagina is retroperitoneal and is surrounded by a quantity of loose connective tissue, a venous plexus, and a variable amount of fat.

=Structure.=—With the exception of the short peritoneal part, as indicated above, the proper wall of the vagina is composed of muscular and mucous coats. The =muscular coat= is composed of a thin layer of longitudinal fibers, and a thicker layer of circular fibers; it contains also many elastic fibers. The =mucous coat= is highly elastic, and is covered with a stratified epithelium. It has no glands.

Under usual conditions the cavity is practically obliterated by apposition of the walls, so that the lumen is a transverse slit; this condition is pronounced when the ampulla of the rectum is full. The anterior end of the vagina is largely occupied by the intravaginal part of the neck of the uterus, so that the cavity is here reduced to an annular recess termed the =fornix vaginæ=. The posterior part is directly continuous with the vulva without any line of demarcation except the valvular fold, which covers the external urethral orifice; in very young subjects this fold is continued on either side, forming the =hymen=, which narrows the entrance to the vagina (Introitus vaginæ).[152]

=Vessels and Nerves.=—The blood-supply is derived from the branches of the =internal pudic arteries=. The =veins= form a plexus which is drained by the =internal pudic veins=. The =lymphatics= pass to the internal iliac lymph glands. The =nerves= are derived from the sympathetic through the pelvic plexus.

THE VULVA

The =vulva= or =urogenital sinus= is the terminal part of the genital tract.[153] It is continuous in front with the vagina, and opens externally at the vulvar cleft below the anus. There is no external line of demarcation between the vagina and vulva. The tube is about five inches (ca. 12 cm.) in length, measured from the external urethral orifice to the inferior commissure; dorsally it is considerably shorter. It is related dorsally to the rectum and anus, ventrally to the pelvic floor, and laterally to the sacro-sciatic ligament, the semimembranosus muscle, and the internal pudic artery. The external orifice or =vulvar cleft= (Rima vulvæ) has the form of a vertical slit, about four to six inches (ca. 10 to 15 cm.) high, and is margined by two prominent rounded folds, the labia. The =labia= of the vulva (Labia vulvæ) meet above at an acute angle, forming the =superior commissure= (Commissura dorsalis), which is about two inches (ca. 5 cm.) below the anus. Below they unite to form the thick rounded =inferior commissure= (Commissura ventralis), which lies about two inches (ca. 5 cm.) behind and below the ischial arch. When the labia are drawn apart, a rounded body, about an inch (ca. 2.5 cm.) wide, is seen in the inferior commissure; this is the =glans clitoridis=, the homologue of the glans penis. Overlying it is a thin fold, the =prepuce= of the clitoris (Præputium clitoridis). At the anterior extremity of the ventral wall of the vulva, _i. e._, about four or five inches (ca. 10 to 12 cm.) from the inferior commissure, is the =external urethral orifice= or meatus urinarius (Orificium urethræ externum). It readily admits the finger and is very dilatable. It is covered by a fold of mucous membrane, the free edge of which is directed backward.

=Structure.=—The =labia= are covered by thin, pigmented, smooth skin, which is richly supplied with sebaceous and sweat glands. This is continuous at a distance of about half an inch (ca. 1 to 1.5 cm.) from the free edge with a thin glandless mucous membrane. Between these is a layer of striped muscle, the =constrictor vulvæ=; this fuses above with the sphincter ani, and embraces the clitoris below, spreading out laterally at the inferior commissure. It constricts the vulvar orifice and elevates the clitoris. The =constrictor vestibuli= muscle embraces the vulva in front of the preceding; it is joined on either side by a band of unstriped muscle which arises from the first and second coccygeal vertebræ, and is homologous with the proximal part of the retractor penis. It constricts the vulva. Under this muscle in the lateral wall is a flattened, oval body, the =bulbus vestibuli= (Fig. 453); this is an erectile structure, homologous with the corpus spongiosum urethræ of the male. It is about two and a half to three inches (ca. 6 to 8 cm.) long, and an inch or more (ca. 3 cm.) wide. It consists of a venous network inclosed in a fibrous capsule, and is supplied with blood by a large branch of the internal pudic artery. The =mucous membrane= of the vulva is reddish in color, and forms longitudinal and transverse folds. It presents ventrally two linear series of small papillæ which converge toward the inferior commissure; these mark the orifices of the ducts of the =glandulæ vestibulares minores=. On either side of the dorsal wall is a group of eight to ten larger prominences on which the ducts of the =glandulæ vestibulares majores= (of Bartholin) open.

Quite exceptionally there may be found on either side of the urethral
orifice the opening of the canals of Gartner (Ductus epoöphori
longitudinales).

The =clitoris= is the homologue of the penis. It arises from the ischial arch by two crura, which unite to form a =body= as large as one’s little finger. This projects backward into the inferior commissure of the vulva, capped by a small rounded =glans=. The organ is composed of erectile tissue similar to the corpus cavernosum penis. The =ischio-cavernosus= (or erector clitoridis) is a very feeble muscle which depresses the clitoris. The veins of the clitoris communicate by an intermediate plexus on either side with the bulbus vestibuli.

THE FEMALE URETHRA

The female =urethra= (Urethra feminina) represents only that part of the canal of the male which lies between the internal urethral orifice and the openings of the ejaculatory ducts. Its length is about two inches (5 cm.), and its lumen is sufficient to admit of the introduction of the finger; it is, however, capable of remarkable dilatation if sufficient care and patience are exercised in the process. It lies centrally on the pelvic floor, and is related and attached dorsally to the vagina.

=Structure.=—The intrinsic =muscular coat= consists of longitudinal and circular layers of unstriped fibers. Between these is a layer of areolar tissue which contains a rich =venous plexus=. The =mucous membrane= is thrown into longitudinal folds when the canal is closed; it is highly elastic, and is covered with stratified epithelium.

The =urethral muscle= (M. compressor urethræ) embraces the urethra and is continued backward for some distance under the constrictor vestibuli. It is covered by a fibro-elastic membrane.

THE MAMMARY GLANDS

The =mammary glands= (Glandulæ lactiferæ) are modified cutaneous glands which are so closely associated functionally with the genital organs as to be considered accessory to them.

In the mare they are two in number, and are placed on either side of the median plane in the inguinal region. Each gland has the form of a short cone, much compressed transversely, and having a flat inner surface. It consists of the glandular mass or body of the gland (Corpus mammæ) and the =teat= or =nipple= (Papilla mammæ). The base is related to the abdominal wall, to which it is attached by areolar tissue, which contains a venous plexus, the superficial inguinal lymph glands, and a variable amount of fat. The apex is constituted by the teat, which is also flattened transversely and varies in length from one to two inches (ca. 2.5 to 5 cm.). Between the bases of the teats is the intermammary groove. On the apex of each teat two or three small orifices are placed close together; these are the openings of the lactiferous ducts.

=Structure.=—The =skin= over the glands is thin, pigmented, chiefly hairless, and supplied with numerous large sebaceous and sweat glands. Under this are two layers of =fascia= except on the teats. The superficial fascia presents no special features. The deep fascia consists of two laminæ detached from the abdominal tunic which descend on either side of the median plane, forming a =septum= between the two glands, and constituting their ligamentum suspensorium.

These laminæ are separated by a layer of areolar tissue, so that it is
possible to remove one gland if diseased by careful dissection between
the layers of the septum.

The =gland substance= or =parenchyma= is pinkish gray in color, and of firmer consistence than the fat which is found around and within the gland. It is inclosed by a fibro-elastic capsule which sends inward numerous trabeculæ; these form the =interstitial tissue=, and divide the gland into =lobes= and =lobules=. In the latter are the secretory =tubules= and =alveoli=, which unite to form the larger =ducts=. Each lobe has a duct, which opens at the base of the teat into a space called the =lactiferous sinus= (Sinus lactiferus); this is lined with mucous membrane, and from it two (or three) =lactiferous ducts= (Ductus lactiferi) pass through the extremity of the nipple. These ducts are lined with a non-glandular mucous membrane, which is covered with stratified squamous epithelium. They are surrounded by unstriped muscular tissue, the bulk of the fibers being arranged in a circular manner to form a =sphincter=.

The size and form of the mammary glands are subject to much variation.
In the young subject, before pregnancy, they are small and contain
little gland tissue. During the latter part of gestation, and
especially during lactation, they increase greatly in size, and the
gland tissue is highly developed. After lactation the secretory
structures undergo marked involution, and the gland is much reduced in
size. The relative amounts of gland substance and interstitial tissue
vary greatly; in some cases a gland of considerable size contains
little secretory tissue and is consequently functionally deficient.

=Vessels and Nerves.=—The =arteries= are derived from the =external pudic artery=, which enters the gland at the posterior part of its base. The =veins= form a plexus on either side of the base of the gland, which is drained by the =external pudic vein= chiefly. The =lymphatics= are numerous and pass chiefly to the superficial inguinal (or supramammary) lymph glands. The =nerves= are derived from the =inguinal nerves= and the =posterior mesenteric plexus= of the sympathetic system.

GENITAL ORGANS OF THE COW

The =ovaries= of the cow are much smaller than those of the mare, measuring usually about one to one and a half inches (ca. 3 to 4 cm.) in length, and a little less than an inch (ca. 2 cm.) in thickness in their largest part. They are oval in form, pointed at the uterine end, and have no ovulation fossa. They are situated usually a little above the middle of the lateral margin of the pelvic inlet in the non-pregnant subject, but may be found a little further forward. They are thus about 16 to 18 inches (ca. 40 to 45 cm.) from the vulva in a cow of medium size. The greater part of the surface of the gland is covered with germinal epithelium, the peritoneal epithelium being limited to a narrow zone along the attached border. Follicles of various sizes are often seen projecting from the surface, as well as corpora lutea; a corpus luteum verum has a pronounced yellow color, and may reach a width of half an inch or more (ca. 1 to 1.5 cm.).

FIG. 411.—OVARY OF COW.

_1_, Broad ligament of uterus; _2_, ligament of ovary; _3_, fimbria
ovarica; _4_, attachment of broad ligament; _5_, surface of ovary
covered with germinal epithelium; _6_, corpora lutea; _7_, Graafian
follicle. (From Leisering’s Atlas.)
]

FIG. 412.—UTERUS OF COW, CONTRACTED, DORSAL VIEW.

_a_, Body of uterus; _b_, _b′_, horn of uterus; c, ovary; _d_, _d′_,
triangular folds connecting horns of uterus (Lig. intercornualia).
(After Zieger.)
]

The =Fallopian= or =uterine tubes= are long and less flexuous than in the mare. The junction with the cornu of the uterus is not so abrupt as in the mare, since the extremities of the horns are pointed. The uterine orifice of the tube is rather large and funnel-shaped. The fimbriæ are not so extensive as in the mare.

The =uterus= lies almost entirely within the abdominal cavity in the adult. The =body= is only about one inch (ca. 2 to 3 cm.) in length, although externally it appears to be much longer. This false impression is due to the fact that the posterior parts of the cornua are united by connective and muscular tissue and have a common peritoneal covering. The =cornua= are, therefore, really longer than they appear externally. They taper gradually toward the free end, so that the junction with the Fallopian tubes is not abrupt, as in the mare. The free part of the horn curves at first downward, forward, and outward, and then turns upward, forming a spiral coil. The =cervix= is about four or five inches (ca. 8 to 10 cm.) long; its wall is remarkably dense, and may be nearly an inch (ca. 2 cm.) in thickness. Its lumen, the =cervical canal=, is spiral, and is ordinarily tightly closed and very difficult to dilate. The =muscular coat= of the uterus is thicker than in the mare. It consists of an external longitudinal layer and two circular strata. The inner circular layer is about a fourth of an inch (ca. 6 mm.) thick in the cervix. The other layers are continued in the vagina. The =mucous membrane= of the horns and body presents as a characteristic feature the =uterine cotyledons= (Cotyledones uterinæ). These are oval prominences, about a hundred in number, which are either irregularly scattered over the surface or arranged in rows of about a dozen.

In the non-gravid uterus they average about ½ to ¾ inch (ca. 15 to 18
mm.) in length, ⅓ inch (ca. 8 mm.) in width, and ⅛ inch (ca. 2 to 4
mm.) in thickness. During pregnancy they become greatly enlarged and
pedunculated. The larger ones then measure about 4 to 5 inches (10 to
12 cm.) in length, 1 to 1½ inches (3 to 4 cm.) in width, and 1 inch (2
to 2.5 cm.) in thickness. The deep face has a hilus at which the
vessels enter. The rest of the surface has a spongy appearance, due to
numerous crypts which receive the villi of the chorion.

The =uterine glands= are long and branched. The mucous membrane of the cervix is pale and forms numerous folds. The latter are arranged in several series which obliterate the lumen. At the external orifice (os uteri) the folds (Plicæ palmatæ) form rounded prominences arranged circularly, which project into the cavity of the vagina. There are no glands in the cervix, but a thick mucus is secreted by goblet cells.

FIG. 413.—UTERINE COTYLEDON OF COW.

The figure represents a cotyledon of medium size. (After Ellenberger,
in Leisering’s Atlas.)
]

FIG. 414.—GENITAL ORGANS OF COW, DORSAL VIEW.

The right uterine cornu and the vagina and vulva are opened up: _1_,
Labium vulvæ; _2_, ventral commissure; _3_, glans clitoridis; _4_,
glandula vestibularis major, exposed by slit in mucous membrane;
_5_, opening of duct of preceding; _6_, suburethral diverticulum;
_7_, external urethral opening; _8_, openings of canals of Gartner;
_9_, os uteri; _10_, corpus uteri; _11_, cornu uteri; _12_,
cotyledons; _13_, Fallopian tube; _14_, ostium abdominale tubæ;
_15_, ovary (From Leisering’s Atlas, reduced.)
]

The =broad ligaments= are not attached in the sublumbar region as in the mare, but to the upper part of the flanks, about a handbreadth below the level of the external angle of the ilium. They contain a conspicuous amount of unstriped muscle. The =round ligaments= are well developed, and can be traced distinctly to the vicinity of the internal inguinal ring.

The =vagina= is somewhat longer and more roomy than that of the mare; its wall is also thicker. Its average length in the non-pregnant animal is about eight inches (ca. 20 cm.); but in the pregnant cow the length increases to twelve inches (30 cm.) or more. The recto-genital pouch of peritoneum extends backward about five inches (ca. 12 cm.) on the dorsal surface, while ventrally the serous coat only extends backward about two inches (ca. 5 cm.).

This gives ample space dorsally for the incision of the fornix vaginæ
in oöphorectomy.

In the ventral wall of the vagina, between the muscular and mucous coats, there are frequently present the two =canals of Gartner= (Ductus epoöphori longitudinales). When well developed they may attain the diameter of a goose quill, and may be traced forward to the anterior part of the vagina or even further. They open posteriorly near the external urethral orifice.

These tubes are remnants of the Wolffian ducts, and, like other fœtal
vestiges, are very variable. Röder states that the right canal was
absent in over 52 per cent., the left in only 22 per cent., of the
cows examined by him. In some cases they may be traced in the broad
ligaments for a variable distance toward the ovary. They are of
clinical interest in that cysts frequently form along their course.

FIG. 415.—DIAGRAMMATIC SAGITTAL SECTION OF PART OF UROGENITAL TRACT OF
COW, SHOWING SUBURETHRAL DIVERTICULUM.
]

The =vulva= has thick wrinkled labia, and both commissures are acute; the lower one is pointed, and has on it a number of long hairs; it lies about two inches (5 cm.) behind, and about the same distance below, the level of the ischial arch. The =glans clitoridis= is small; the =crura= are about four inches (ca. 10 cm.) long and are flexuous. The =external urethral orifice= or meatus urinarius is four or five inches (10 to 12 cm.) from the ventral commissure. Beneath it is a blind pouch, the =suburethral diverticulum=, which is more than an inch (ca. 3 to 4 cm.) long, and readily admits the end of a finger.

The form and position of this pouch should be carefully noted on
account of the difficulty it causes in catheterizing the bladder. If
the catheter is passed along the ventral wall of the vulva (as in the
mare), it will always enter the pouch instead of the urethra.

The =glandulæ vestibulares majores= (or glands of Bartholin) are situated on the lateral walls of the vulva, under the constrictor vulvæ. They are little over an inch (ca. 3 cm.) long and about half an inch (ca. 1.5 cm.) in width. Each has a single duct which opens about an inch and a half (ca. 3 to 4 cm.) lateral to and behind the external urethral orifice.

The =urethra= of the cow is about four inches (10 cm.) in length; it is narrower and much less dilatable than that of the mare. It is fused dorsally with the wall of the vagina, while laterally and ventrally it is covered by the constrictor vaginæ muscle.

The =mammary glands=, normally two in number, are popularly termed the udder. They are very much larger than in the mare, and the body of each is somewhat ellipsoidal in form, but flattened transversely. The =base= (or dorsal surface) of each gland is slightly concave and slopes obliquely downward and forward in adaptation to the abdominal wall, to which it is adherent; posteriorly it is in relation to the large supramammary lymph glands and a quantity of fat. The inner surface is flat, and is separated from the other gland by a well-developed double septum. The outer surface is convex. Four well-developed teats are present; they average about three inches (ca. 7 to 8 cm.) in length. It is customary to consider the udder to consist of four “quarters.” There is no septum nor visible division between the two quarters of the same side, but, on the other hand, injections of fluids of different colors into the two teats of the gland demonstrate that the cavities drained by them do not communicate.

FIG. 416.—CROSS-SECTION OF MAMMARY GLANDS OF COW.

_a_, Body of gland; _b_, lactiferous sinus; _c_, cavity of teat; _d_,
duct of teat; _e_, intermammary groove; _f_, septum between glands;
_g_, supramammary fat.
]

The size and form of the glands vary greatly; in the highly
specialized dairy breeds (_e. g._, Holsteins) they often attain
enormous dimensions. The size of the udder is not a certain index of
its productivity, since some so-called “fleshy” udders contain a very
large amount of interstitial tissue and relatively little parenchyma.
Small accessory teats often occur posteriorly; commonly these are
rudimentary and imperforate (polythelia), but sometimes they drain a
small amount of gland substance (polymastia). Sanson described a case
in which there were seven teats, all giving milk.

Each teat has a single duct which widens superiorly and opens freely into a roomy =lactiferous sinus= or milk cistern (Sinus lactiferus). The =lactiferous duct= or teat canal is lined by a glandless mucous membrane which is covered with stratified squamous epithelium; the lower part (ca. 1 cm.) of the canal is narrow, and is closed by a =sphincter= of unstriped muscle. The =mucous membrane= of the sinus forms numerous folds which render the cavity multilocular.

=Vessels and Nerves.=—The blood-supply is derived from the =external pudic arteries=. The =veins= form a circle at the base of the udder, from which the blood is drained by three trunks, viz., the very large =subcutaneous abdominal= (“milk vein”), the =external pudic=, and the =perineal vein=. The =lymphatics= are numerous, and pass to the supramammary glands chiefly. The nerves are derived from the =inguinal nerves= and the =posterior mesenteric plexus= of the sympathetic.

GENITAL ORGANS OF THE SOW

FIG. 417.—GENITAL ORGANS OF SOW, DORSAL VIEW. THE VAGINA AND CERVIX
UTERI ARE SLIT OPEN.

_1_, Labia vulvæ; _2_, glans clitoridis; _3_, vulva; _4_, external
urethral orifice; _5_, vagina; _5′_, cervix uteri; _6_, corpus
uteri; _7_, cornua uteri, one of which is opened at _7′_ to show
folds of mucous membrane; _8_, Fallopian tube; _8′_, abdominal
opening of tube; _9_, ovaries; _10_, ovarian bursa; _11_, broad
ligaments of uterus; _12_, urinary bladder. (From Leisering’s
Atlas.)
]

The =ovaries= are concealed in the bursa ovarii, owing to the large extent of the mesosalpinx. They are more rounded than in the bitch, and have a distinct hilus. They are situated usually as in the cow, but their position is quite variable in animals which have borne young. The surface commonly presents rounded prominences, so that sometimes the gland has an irregular, mulberry-like aspect; this is due to the fact that there is very little stroma and the larger Graafian follicles project from the surface.

The =Fallopian= or =uterine tubes= are long (ca. 15 to 30 cm.), and less flexuous than in the mare. The fimbriated extremity forms an ampulla and has a large abdominal opening. The uterine end shades insensibly into the small extremity of the cornu of the uterus.

The =uterus= presents several striking features. The =body= is only about two inches (ca. 5 cm.) long. The =horns= are extremely long and flexuous, and are freely movable, on account of the large extent of the broad ligaments. The extremities of the horns taper to about the diameter of the Fallopian tubes.[154] The =neck= is remarkable for its length (ca. 15 to 20 cm.) and the fact that it is directly continued by the vagina without forming any intravaginal projection (os uteri). It can be distinguished by the transverse folds of its mucous membrane and the thickness of its wall.

The changes in form and position of the uterus during pregnancy are
similar to those mentioned later in the case of the bitch.

The =vagina= is about four or five inches (ca. 10 to 12 cm.) long in a sow of medium size. It is small in caliber, and has a thick muscular coat which consists mainly of circular fibers. The mucous membrane is plicated, and is intimately united with the muscular coat.

The =vulva= is relatively long. The inferior commissure is pointed and dependent. The mucous lining is plicated. There is a small =suburethral diverticulum=. The vestibular glands are small and variable in number. The vestibular bulbs are little developed. The canals of Gartner may sometimes be traced as far as the ovary, but are often difficult to find.

The =clitoris= is long, flexuous, and pointed; beneath it is a cul-de-sac.

The =urethra= is very long; its vulvar orifice is not concealed by a valvular fold.

The =mammary glands= are usually ten or twelve in number, and are arranged in two rows, as in the bitch. Each teat has commonly two excretory ducts.

GENITAL ORGANS OF THE BITCH

The =ovaries= (Fig. 336) are small, elongated-oval in outline, and flattened. Each ovary is situated close to or in contact with the posterior pole of the corresponding kidney, and thus lies ventral to the third or fourth lumbar vertebræ, or about half-way between the last rib and the crest of the ilium. Each is concealed in a peritoneal pouch, the =bursa ovarii=, which has a slit-like opening ventrally. The two folds which form this pouch contain a quantity of fat and unstriped muscle. They are continued to the cornu of the uterus, constituting the =mesosalpinx= and the =ovarian ligament=. The surface of the ovary presents prominences caused by projecting Graafian follicles. There is no distinct hilus.

The =Fallopian= or =uterine tubes= are small and average two or three inches (ca. 5 to 8 cm.) in length. Each passes at first forward and then turns backward, having a straight or only slightly flexuous course. The fimbriated extremity lies in the bursa ovarii, and has a rather large opening. The uterine orifice is very small.

The =uterus= has a very short body and two long narrow horns. In a bitch of medium size the body is about an inch (ca. 2 to 3 cm.) and the cornua five or six inches (ca. 12 to 15 cm.) long. The horns are of uniform diameter, are nearly straight, and lie entirely within the abdomen. They diverge from the body in the form of a V toward each kidney. Their posterior parts are united by the peritoneum. The neck is very short and is fused dorsally with the vagina. It has a thick muscular coat. The mucous membrane of the uterus has long uterine glands and also short tubular crypts.

The =broad ligaments= contain fat and unstriped muscle. They are much longer in the middle than at either end. The posterior part is attached to the anterior part of the vagina. The =round ligaments= are very long, extending through the inguinal canals, and traceable almost to the vulva.

The horns of the gravid uterus present dilatations or =ampullæ=, which
contain the fœtuses, and are separated by constrictions. The gravid
uterus lies on the ventral abdominal wall, and toward the end of
gestation extends forward to the stomach and liver.

The =vagina= is relatively long. It is narrow anteriorly, and has no distinct fornix. The muscular coat is thick and consists chiefly of circular fibers. The mucous membrane forms longitudinal folds. The canals of Gartner are usually absent.

FIG. 418.—GENITAL ORGANS OF BITCH.

Vulva, vagina, and uterus (in part) are slit open. _a_, Ovarian bursa;
_b_, same opened to show the right ovary, _c_; _d_, _d_, horns of
uterus; _e_, _e′_, body of uterus; _f_, neck of uterus; _f′_, os
uteri; _g_, vagina; _h_, hymen; _i_, vulva; _k_, external urethral
orifice; _l_, urinary bladder; _m_, urethra; _n_, _n_, labia vulvæ;
_o_, fossa clitoridis; _p_, clitoris. (After Ellenberger, in
Leisering’s Atlas.)
]

The =vulva= has thick labia which form a pointed inferior commissure. The mucous lining is smooth. On either side of the urethral orifice there is a small depression. The glandulæ vestibulares majores are absent, but the smaller glands are present, and their ducts open ventrally on either side of a median ridge. The vestibular bulbs are relatively large and join dorsally. The clitoris has a small pointed glans, beneath which is a diverticulum. The corpus cavernosum is a little more than an inch (ca. 3 to 4 cm.) long in a subject of medium size, and is infiltrated with fat.

The =mammary glands= are usually ten in number, and are arranged in two series extending from the posterior part of the pectoral region to the inguinal region; they are, therefore, designated according to location as =pectoral=, =abdominal=, and =inguinal=. The teats are short, and present on their apices six to twelve small orifices of the excretory ducts.

ANGIOLOGY: THE VASCULAR SYSTEM

=Angiology= is the description of the organs of circulation of the blood and lymph—the heart and vessels. The =heart= is the central hollow muscular organ which functions as a suction and force pump; the differences in pressure caused by its contraction and relaxation determine the circulation of the blood and lymph. It is situated in the middle mediastinal space of the thorax, between the two lungs, and is inclosed in a fibro-serous sac—the pericardium. The vessels are tubular and run through almost all parts of the body. They are designated according to their contents as =blood-= and =lymph vessels=.

The =blood-vascular system= consists of: (1) the =arteries=, which convey blood from the heart to the tissues; (2) the =capillaries=, microscopic tubes in the tissues which permit of the necessary interchange between the blood and the tissues; (3) the =veins=, which convey the blood back to the heart.

The blood-vessels are divided into the =pulmonary= and the =systemic=. The =pulmonary artery= conveys the blood from the right ventricle of the heart to the lungs, where it is arterialized, and is returned by the =pulmonary veins= to the left atrium of the heart, and passes into the left ventricle. The =systemic arteries= convey the blood from the left ventricle all over the body, whence it is returned by the =venæ cavæ= to the right atrium, and passes into the right ventricle.

It should be noted, however, that the lungs receive arterial blood
through the systemic bronchial arteries. This blood is returned in
part by the bronchial veins to the right atrium (indirectly), in part
by the pulmonary veins to the left atrium.

The term =portal system= is often applied to the portal vein and its tributaries which come from the stomach, intestine, pancreas, and spleen. The vein enters the liver, where it branches like an artery, so that the blood in this subsidiary system passes through a second set of capillaries before being conveyed to the heart by the hepatic veins and the posterior vena cava.

The =arteries= (Arteriæ), as a rule, divide at an acute angle, giving off finer and finer branches. In some cases branches come off at a right angle, and others are recurrent, _i. e._, run in a direction opposite to that of the parent stem. The intercommunication of branches of adjacent arteries is termed =anastomosis=. Most commonly the connections are made by a network of numerous fine branches (Plexus vasculosus). Relatively large communicating branches (Rami communicantes) occur in certain places; they may be transverse or in the form of arches. Wide-meshed networks of vessels are termed =Retia vasculosa=. =Terminal= or =end arteries= are such as form isolated networks, _i. e._, do not anastomose with adjacent arteries. A =rete mirabile= is a network intercalated in the course of an artery. A =collateral vessel= (Vas collaterale) is one which pursues a course near and similar to that of a larger vessel.

The =veins= (Venæ) are in general arranged like the arteries, but are usually of greater caliber. When a vein accompanies an artery, it is termed a =vena comitans= or =satellite vein=; in many places two veins accompany a single artery. The primitive venous trunks do not run with the arteries, and most of the superficial veins (Venæ cutaneæ) pursue independent courses. They anastomose even more freely than the arteries, and large communicating branches are very common. The veins form very rich plexuses (Plexus venosi) in many places. Some veins which are without independent walls and are inclosed by dense membranes and run usually in bony grooves are termed (venous) =sinuses=; examples of this are the sinuses of the dura mater of the brain.

=Structure of Arteries.=—The wall consists of three coats. The =external coat= (Tunica externa) consists chiefly of fibrous connective tissue. In the deeper part are some elastic fibers, and in some arteries there are also longitudinal unstriped muscle-fibers. The =middle coat= (Tunica media) is composed of unstriped muscle and elastic tissue in medium-sized arteries. In small vessels there is only the muscular tissue, and in the largest trunks only elastic tissue. The =internal coat= or =intima= (Tunica intima) consists of a layer of endothelial cells, resting on an elastic membrane. The =sheath= (Vagina vasis) is a condensation of the surrounding connective tissue, and is attached more or less closely to the external coat.

=Structure of Veins.=—The walls of veins are similar in structure to those of the arteries, but are very much thinner, so that veins collapse more or less completely when empty, while arteries do not. The =middle coat= is very thin and consists to a large extent of ordinary connective tissue. The =intima= is also less elastic than in the arteries. In many veins this coat forms semilunar =valves=, the free edges of which are directed toward the heart. They are most numerous in the veins of the skin and the deep veins of the extremities (except the foot), while in most veins of the body cavities and viscera they are absent or occur only where the veins open into larger ones or where two veins join.

The walls of the vessels are supplied with blood by numerous small arteries, called =vasa vasorum=. These arise from branches of the artery which they supply or from adjacent arteries, ramify in the external coat, and enter the middle coat also.

The =nerves= of the vessels consist of both medullated and non-medullated fibers. They form plexuses around the vessels, from which fibers pass mainly to the muscular tissue of the middle coat.

BLOOD-VASCULAR SYSTEM OF THE HORSE

THE PERICARDIUM[155]