Chapter V (3)

124. The organs which belong to the apparatus of digestion are—1. The stomach (fig. LXIII. 2) 2. The duodenum (fig. LXIII. 4). 3. The jejunum (fig. LXIII. 5). 4. The ilium (fig. LXIII. 5). The three last organs are called the small intestines, and their office is partly to carry on the digestion of the aliment commenced in the stomach, and partly to afford an extended surface for the absorption of the nutriment as it is prepared from the aliment. 5. The pancreas (fig. LXIV. 5). 6. The liver (fig. LXIV. 2). 7. The spleen (fig. LXIV. 4). The three last organs truly belong to the apparatus of digestion, and their office is to co-operate with the stomach and the small intestines in the conversion of the aliment into nutriment.

1. Esophagus; 2. stomach; 3. liver raised, showing its under surface; 4. duodenum; 5. small intestines; 6. cæcum; 7. colon; 8. urinary bladder; 9. gall bladder; 10. abdominal muscles divided and reflected.]

125. The organs which belong to the apparatus of excretion are—1. The large intestines consisting of the cæcum (fig. LXIII. 6). 2. The colon (fig. LXIII. 7). 3. The rectum (fig. LXIV. 10). It is the office of these organs, which are called the large intestines, to carry out of the system that portion of the alimentary mass which is not converted into nourishment. 4. The kidneys (fig. LXIV. 6), the organs which separate in the form of the urine an excrementitious matter from the blood, in order that it may be conveyed out of the system.

General view of the viscera of the abdomen. 1. Stomach raised; 2. under surface of liver; 3. gall bladder; 4. spleen; 5. pancreas; 6. kidneys; 7. ureters; 8. urinary bladder; 9. portion of the intestine called duodenum; 10. portion of the intestine called rectum; 11. the aorta.]

126. The last division of the trunk, called the pelvis (fig. LXI. 3), consists of a circle of large and firm bones, interposed between the lower portion of the trunk and the inferior extremities (fig. XLV.). The bones that compose the circle, distinct in the child, are firmly united in the adult into a single piece; but as the original separation between each remains manifest, they are always described as separate bones. They are the sacrum (fig. XLV. 5), the coccyx (fig. XXXV.), the ilium (fig. XLV. 11), the ischium (fig. XLV. 12), and the pubis (fig. XLV. 13).

127. The sacrum, placed like a wedge between the moveable portion of the spinal column and the lower extremities, forms the posterior boundary of the pelvis. The figure of this bone is triangular (fig. XLV. 5); its anterior surface is concave and smooth, for enlarging the cavity of the pelvis and sustaining the organs contained in it (fig. XLV. 5); its posterior surface is convex, irregular, and rough (fig. XXXV.), giving origin to the great muscles that form the contour of the hip, and to the strong muscles of the back and loins that raise the spine and maintain the trunk of the body erect.

128. The base or upper part of the sacrum receives the last vertebra of the loins on a large and broad surface (fig. XLV. 4), forming a moveable joint; and the degree of motion at this point is greater than it is at the higher points of the spinal column. Firmly united at its sides with the haunch bones, it admits there of no degree of motion.

129. The coccyx, so named from its resemblance to the beak of the cuckoo, when elongated by a succession of additional bones, forms the tail in quadrupeds; but in man it is turned inwards to support the parts contained in the pelvis, and to contract the lower opening of the cavity. By means of a layer of cartilage, the medium by which this bone is connected with the sacrum, it forms a moveable articulation, continuing moveable in men until the age of twenty-five, and in women until the age of forty-five; continuing moveable in women thus long, in order that by yielding to the force which tends to push it backwards during the period of labour, it may enlarge the lower aperture of the pelvis, and so facilitate the process of parturition and diminish its suffering.

130. The lateral boundaries of the pelvis are formed by the ilium, the haunch bone (fig. XLV. 11), and by the ischium, the hip bone (fig. XLV. 12). The ilium forms the lower part of the abdomen and the upper part of the pelvis (fig. XLV. 11); its broad expanded wing supports the contents of the abdomen, and gives attachment to the muscles that form the anterior portion of its walls (figs. XLV. 11, and LXIII. 9); its external convex surface sustains the powerful muscles that extend the thigh; and along its internal surface is the prominent line which marks the brim of the pelvis (fig. XLV. 15), and which divides this cavity from that of the abdomen.

131. The ischium or hip bone is the lower part of the pelvis (fig. XLV. 12); at its undermost portion is a rounded prominence called the tuberosity (fig. XLV. 12), in its natural condition covered with cartilage, upon which is superimposed a cushion of fat. It is this part on which the body is supported in a sitting posture.

132. The pubis or share bone forms the upper and fore part of the pelvis (fig. XLV. 13), and together with the two former bones, completes the large and deep socket, termed the acetabulum (fig. XLV. 14), into which is received the head of the thigh-bone (fig. XXXIV. 4). The margin of the acetabulum and the greater part of its internal surface is lined with cartilage, so that in its natural condition it is much deeper than it appears to be when the bones alone remain.

133. The lower aperture of the pelvis, which appears large when all the soft parts are removed, is not really large, for in its natural state it is filled up partly by muscles and partly by ligaments, which sustain and protect the pelvic organs, leaving only just space enough for the passage to and from those which have their opening on the external surface.

134. The cavity of the pelvis, together with all the organs contained in it, are lined by a continuation of the membrane that invests the abdomen and its contents.

135. The organs contained in the pelvis are the rectum (fig. LXIV. 9), which is merely the termination of the large intestines, the urinary bladder (fig. LXIV. 8), and the internal part of the apparatus of reproduction.

136. The large and strong bones of the pelvis not only afford lodgment and protection to the tender organs contained in its cavity, but sustain the entire weight of the body, the trunk resting on the sacrum as on a solid basis (fig. XLV. 5), and the lower extremities being supported in the sockets in which the heads of the thigh-bones play, in the varied movements of locomotion (fig. XXXIV. 4).

137. The last division of the body comprehends the superior and the inferior extremities.

138. The superior extremities consist of the shoulder, arm, fore-arm, and hand.

139. The soft parts of the SHOULDER are composed chiefly of muscles; its bones are two, the scapula or the _blade bone_, and the clavicle or the _collar bone_ (fig. LXV. 2, 4).

1. Sternum; 2. clavicle; 3. ribs; 4. anterior surface of scapula; 5. coracoid process of scapula; 6. acromion process of scapula; 7. margin of glenoid cavity of scapula; 8. body of the humerus or bone of the arm; 9. head of the humerus.]

140. The SCAPULA is placed upon the upper and back part of the thorax, and occupies the space from the second to the seventh ribs (fig. LXV. 4)

1. Posterior surface of scapula; 2. margin of scapula; 3. acromion process; 4. margin of glenoid cavity; 5. clavicle; 6. body of humerus; 7. head of humerus.]

Unlike that of any other bone of the body, it is embedded in muscles, without being attached to any bone of the trunk, excepting at a single point. From the bones of the thorax it is separated by a double layer of muscles, on which it is placed as upon a cushion, and over the smooth surface of which it glides. Originally, like the bones of the skull, it consisted of two tables of compact bone, with an intermediate layer of spongy bony substance (diploë); but, by the pressure of the muscles that act upon it, it gradually grows thinner and thinner, until, as age advances, it becomes in some parts quite transparent and as thin as a sheet of paper.

141. The figure of the scapula is that of an irregular triangle (fig. LXVI.). Its anterior surface is concave (fig. LXV. 4), corresponding to the convexity of the ribs (fig. XLV. 7); its posterior surface is very irregular (fig. LXVI. 1), being in some parts concave and in others convex, giving origin especially to two large processes (figs. LXV. 5, and LXVI. 3); one of which is termed the _acromion_ (fig. LXVI. 3), and the other the _coracoid_ process of the scapula (fig. LXV. 5). The margins of the bone, whatever the thinness of some portions of it, are always comparatively thick and strong (fig. LXVI. 2), affording points of origin or of insertion to powerful muscles. At what is called the anterior angle of the bone there is a shallow oval depression covered with cartilage and deepened by a cartilaginous margin, called the _glenoid_ cavity of the scapula (figs. LXV. 7, and LXVI. 4), which receives the head of the humerus or bone of the arm (figs. LXV. 9, and LXVI. 7, 6).

142. The clavicle, the second bone of the shoulder, is a long and slender bone, of the form of an italic , projecting a little forwards towards its middle, so as to give a slight convexity of outline to the top of the chest and the bottom of the neck (fig. LXV. 2). It is attached by one extremity to the sternum (fig. LXV. 2) and by the other to the scapula (fig. LXV. 2), by moveable joints. The nature of an immoveable joint has been explained (63). In the connexion of the bones of the trunk, while the main object is to secure firmness of attachment, some degree of motion is at the same time obtained (81 et seq.): but the mode in which the several bones of the extremities are connected with each other and with the trunk, admits of so great a degree of motion, that these articulations are pre-eminently entitled to the name of moveable joints. The component parts of all moveable joints are bone, cartilage, synovial membrane, and ligament. The great character of a moveable joint is the approximation of two or more bones; yet these bony surfaces are never in actual contact, but are invariably separated from each other by cartilage. The cartilage either covers the entire extent of the articulating surface of the bones, as in the shoulder-joint, where both the head of the humerus and the cavity of the scapula that receives it are enveloped in this substance (fig. LXV. 7. 9), or a portion of it is placed between the articulating surfaces of the bones, as in the joint between the clavicle and sternum (fig. LXVII. _a_); which, when so placed, is termed an interarticular cartilage (fig. LXVII. _a_). By its smooth surface cartilage lessens friction; while by its elasticity it facilitates motion and prevents concussion. Slightly organized cartilage is provided with comparatively few blood-vessels and nerves. Had it been vascular and sensible like the skin and the muscle, the force applied in the movements of the joint would have stimulated the blood-vessels to inordinate action, and the sensibility of the nerves would have been the source of constant pain: every motion of every joint would have been productive of suffering, and have laid the foundation of disease. The facility and ease of motion obtained by the smoothness, elasticity, and comparative insensibility of cartilage are still further promoted by the fluid which lubricates it, termed synovia, secreted by a membrane called synovial, which lines the internal surface of the joint, and which bears a close resemblance to the serous (30). Synovia is a viscid fluid of the consistence of albumen (5). It is to the joint what oil is to the wheel, preventing abrasion and facilitating motion; but it is formed by the joint itself, at the moment when needed, and in the quantity required. The motion of the joint stimulates the synovial membrane to secretion, and hence the greater the degree of motion, the larger the quantity of lubricating fluid that is supplied. The several parts of the apparatus of moveable joints are retained in their proper position by ligamentous substance, which, as has been shown (96 and 97), is oftentimes so strong that it is easier to fracture the bone than to tear the ligament, and in every case the kind and extent of motion possessed by the joint are dependent mainly on the form of the articulatory surfaces of the bones and on the disposition of the ligaments.

143. In the joint formed by the clavicle and the sternum (fig. LXVII. _a_) an interarticular cartilage is placed between the two bones which are united, first by a strong fibrous ligament, which envelops them as in a capsule (fig. LXVII. 1); by a second ligament, which extends from the cartilage of the first rib to the clavicle (fig. LXVII. 4), by which the attachment of the clavicle to the sternum is materially strengthened; and by a third ligament which passes transversely from the head of one clavicle to that of the other (fig. LXVII. 3). The joint thus formed, though so strong and firm that the dislocation of it is exceedingly rare, yet admits of some degree of motion in every direction, upwards, downwards, forwards, and backwards; and this articulation is the sole point by which the scapula is connected with the trunk, and consequently by which the upper extremity can act, or be acted upon, by the rest of the body.

1. The fibrous capsule of the sternum and clavicle; 2. the same laid open, showing _a_, the interarticular cartilage; 3. the ligament connecting the two clavicles; 4. the ligament joining the clavicle to the first rib; 5. ligaments passing down in front of the sternum.]

144. The scapular extremity of the clavicle (fig. LXVIII. 6) is attached to the processes of the scapula (fig. LXVIII. 4. 3) by several ligaments of great strength (fig. LXVIII. 7, 8, 9). First by very strong fasciculi which pass from the upper surface of the clavicle to the acromion of the scapula (fig. LXVIII. 6); and secondly by two ligaments which unite the clavicle with the coracoid process of the scapula (fig. LXVIII. 8, 9). These ligaments are so powerful that they resist a force capable of fracturing the clavicle; and they need to be thus strong, for the clavicle is a shaft which sustains the scapula, and through the scapula the whole of the upper extremity; and the main object of the joint by which these bones are united, is to afford a firm attachment of the scapula to its point of support.

1. The clavicle; 2. the anterior part of the scapula; 3. the coracoid process; 4. the acromion process; 5. the humerus; 6. ligaments binding the scapular end of the clavicle to the acromion; 7. 8. 9. ligaments passing from one process of the scapula to the other; 10. the fibrous capsule of the shoulder-joint.]

145. The clavicle serves the following uses: it sustains the upper extremity; it connects the upper extremity with the thorax; it prevents the upper extremity from falling forwards upon the thorax; and it affords a fixed point for steadying the extremity in the performance of its various actions.

146. The glenoid cavity of the scapula (fig. LXV. 7) receives the head of the humerus, the bone of the arm (fig. LXV. 9), and the two bones being united by ligament form the shoulder-joint (fig. LXVIII.). This joint is what is termed a ball and socket joint, the peculiarities of which are two: first, beyond all others this mode of articulation admits of free and extensive motion; in the present case, there is the utmost freedom of motion in every direction, upwards, downwards, backwards, and forwards. In the second place, this mode of articulation admits of the motion of the limb without that of the body, or of the motion of the body without that of the limb. When at rest, the arm may be moved in almost any direction without disturbing the position of any other part of the frame; the manifold advantages of which are obvious. On the other hand, by careful management, very considerable variations in the posture of the body may be effected without the communication of any degree of motion to the limb; an unspeakable advantage when the limb has sustained injury, or is suffering from disease.

147. It does not seem possible to construct a joint of great strength, capable, at the same time, of the degree of motion possessed by the joint of the shoulder. So shallow is the socket of the scapula, and so large the head of the humerus, that it seems as if the slightest movement must dislodge it from its cavity (fig. LXVI. 4. 7). For sustaining heavy weights or resisting a great amount of pressure, applied to it suddenly and in various directions, the arm is obviously unfitted. But this is not its office. The superior extremities are the organs of apprehension—the instruments by which the mind executes the commands of the will. They do not need the strength required by the organs that sustain the weight of the body and that perform the function of locomotion; but they do need freedom and extent of motion: to this strength may be sacrificed, and so it is; yet what can be done to combine strength with mobility is effected. Large and strong processes of bone, proceeding as has been shown (141), from the convex surface of the scapula (figs. LXV. and LXVI.), overhang, and to a considerable extent surround, the head of the arm-bone, especially resisting the force that would dislodge it from its socket and drive it upwards, inwards, and backwards (fig. LXV.), the directions in which force is most commonly applied to it. By these processes of bone the joint is greatly strengthened, especially in those directions. Moreover, a strong ligament, termed the fibrous capsule (fig. LXVIII. 10) envelops the joint. This ligament, arising from the neck of the scapula (fig. LXVIII. 10), expands itself in such a manner as completely to surround the head of the humerus (fig. LXVIII. 10); and then again contracts in order to be inserted into the neck of the bone (fig. LXVIII. 10). This ligament is strengthened by the tendons of no less than four muscles which are expanded over it, as well as by the powerful substance termed fascia which is reflected upon it from both the processes and ligaments of the scapula. In addition to all these expedients for fortifying the joint, it receives a further security in the position of the scapula, which is loose and unattached; which slides easily over the ribs upon its cushion of flesh; which thus obtains, by its facility of yielding, some compensation for its want of strength, eluding the force which it cannot resist.

148. The arm consists of numerous and powerful muscles, and of a single bone, the humerus, which belongs to the class of bones termed cylindrical (185).

149. The upper end of the humerus terminates in a circular head (fig. LXV. 9), which is received into the socket of the scapula (fig. LXV. 9. 7) termed, as has been stated (141), its glenoid cavity. The middle portion of the bone, or what is termed its shaft (fig. LXV. 8), diminishes considerably in magnitude, and becomes somewhat rounded (fig. LXV. 8), while its lower end again enlarges, and is spread out into a flattened surface of great extent (fig. LXIX. 1, 3, 2, 4). Of this broad flattened surface, the middle portion is grooved (fig. LXIX. 2): it is covered with cartilage; it forms the articulating surface by which the arm is connected with the fore-arm. On each side of this groove there is a projection of bone or tubercle, termed condyle (fig. LXIX. 3, 4), the inner (fig. LXIX. 3) being much larger than the outer (fig. LXIX. 4). The inner condyle gives origin to the muscles that bend, the outer to those that extend the fore-arm and the fingers (figs. LXXXIV. 1, 2, and LXXXV. 1).

1. Lower extremity of the humerus; 2. grooved surface; 3. internal condyle; 4. external condyle; 5. the upper part of the ulna; 6. the head; 7. the neck; 8. the tubercle of the radius.]

150. The muscles that act upon the arm arise from the back (fig. LXXII. 2), the chest (fig. LXXI. 1), the clavicle (fig. LXXI. 1), and the scapula (fig. LXXI. 3); and they move the arm with freedom and power upwards, downwards, forwards, backwards, inwards, and outwards. The chief muscle that raises the arm is the deltoid (fig. LXXI. 3), which arises partly from the clavicle and partly from the scapula (fig. LXXI. 3). It has the appearance of three muscles proceeding in different directions, the different portions being separated by slight fissures (figs. LXXI. 3, and LXXII. 3). The fibres converging unite and form a powerful muscle which covers the joint of the humerus (fig. LXXI. 3). It is implanted by a short and strong tendon into the middle of the humerus (fig. LXXI. 4). Its manifest action is to pull the arm directly upwards. Its action is assisted by the muscles that cover the back of the scapula, which are in like manner inserted into the humerus, and which, at the same time that they elevate the arm, support it when raised.

View of the muscles on the fore part of the chest that act upon the arm. 1. The muscle called the great pectoral; 2. the small pectoral; 3. the deltoid; 4. the humerus.]

151. The principal muscle that carries the arm downwards is the latissimus dorsi (fig. LXXII. 2), the broadest muscle of the body, which, after having covered all the lower part of the back and loins, terminates in a thin but strong tendon which stretches to the arm, and is implanted into the humerus (fig. LXXII. 2), near the tendon of a muscle immediately to be described,—the great pectoral. When the arm is raised by the deltoid and its assistant muscles, the latissimus dorsi carries it downwards with force, and its powerful action is increased by that of other muscles which arise from the scapula and are inserted into the arm.

152. The principal muscle that carries the arm forwards towards the chest, is the great pectoral (fig. LXXI. 1), which, arising partly from the clavicle (fig. LXXI. 1), partly from the sternum (fig. LXXI. 1), and partly from the cartilages of the second, third, fourth, fifth, and sixth ribs (fig. LXXI. 1), covers the greater part of the breast (fig. LXXI. 1). Its fibres, converging, terminate in a strong tendon, which is inserted near the tendon of the longissimus dorsi into the humerus, about four inches below its head (fig. LXXI. 1). These two muscles form the axilla or armpit, the anterior border of the axilla consisting of the pectoral muscle. Though each of these muscles has its own peculiar office, yet they often act in concert, thereby greatly increasing their power, and the result of their combined action is to carry the arm either directly downwards or to the side of the chest.

View of the muscles seated on the back part of the trunk that act upon the shoulder and arm. 1. The muscle called the trapezius; 2. the latissimus dorsi; 3. the deltoid.]

153. Some of the muscles that elevate the arm carry it inwards, and others outwards; the muscles that carry it forwards likewise carry it inwards; while of the muscles that pull it downwards, some direct it forwards and inwards, and others backwards and outwards (151 and 152).

154. It has been already stated that the shoulder-joint is completely surrounded by the muscular fibres or the tendinous expansions of several of these powerful muscles, which have a far greater effect in maintaining the head of the humerus in its socket than the fibrous capsule of the joint; the latter being necessarily loose, in order to allow of the extended and varied motions of the arm, whereas the muscles that encompass the joint adhere closely and firmly to it. Moreover, by virtue of their vital power these muscles act with an efficiency which a mere ligamentous band is incapable of exerting; for they apportion the strength of resistance to the separating force, and react with an energy proportioned to the violence applied.

155. The bones of the fore-arm are two, the ulna and the radius (figs. LXIX. and LXXIII.). The ulna is essentially the bone of the elbow (figs. LXIX. 5, and LXXIII. 3); the radius that of the hand (fig. LXXV.). Supposing the arm to hang by the side of the body, and the palm of the hand to be turned forwards, the ulna, in apposition with the little finger, occupies the inner; and the radius, in apposition with the thumb, occupies the outer part of the fore-arm (fig. XXXIV. 3).

1. The internal condyle of the humerus; 2. the external
condyle of the humerus; 3. the olecranon process of the ulna;
4. the head of the radius.]

156. The upper end of the ulna belonging to the elbow is large (figs. LXIX. 5, and LXXIII. 3). It sends backwards the large projection commonly named the elbow or _olecranon_ (fig. LXXII. 3), in the centre of which there is a smooth and somewhat triangular surface (fig. LXXIII. 3) which is always covered by skin of a coarse texture, like that placed over the lower part of the knee-pan, as if nature intended this for a part on which we may occasionally lean and rest. Large at the elbow, the ulna gradually grows smaller and smaller as it descends towards the wrist, where it ends in a small round head (fig. LXXXII. 2), beyond which, on the inner side, or that corresponding to the little finger, it projects downwards a small rounded point, termed the styloid process (fig. LXXXII. 3). As the styloid process and the olecranon, the two extremities of the ulna (figs. LXXIII. 3, and LXXII. 3), are easily and distinctly felt, the length of this bone was primitively used as a measure, called a cubit, which was the ancient name of the bone.

157. The radius, the second bone of the fore-arm, placed along its outer part next the thumb, is small at its upper end (figs. LXIX. 6, and LXXIII. 4); but its body is larger than that of the ulna; while its lower end, next the wrist to which it properly belongs, is very bulky (fig. LXXXII. 1). Its upper end is formed into a small circular head, which is united by distinct joints both to the humerus and to the ulna (fig. LXIX. 6). The top of its rounded head is excavated into a shallow cup (figs. LXIX. 6, and LXXIII. 4) which receives a corresponding convexity of the humerus (fig. LXIX. 2), and its lower extremity is excavated into an oblong cavity, which receives two of the bones of the wrist (fig. LXXXIII. 1. 4).

158. The joint of the elbow is composed above of the condyles of the humerus (fig. LXIX. 3. 2), and below by the heads of the ulna and radius (fig. LXIX. 5. 6).

159. The upper surface of the ulna is so accurately adapted to the lower surface of the humerus that the one seems to be moulded on the other (figs. LXIX. 5, and LXXIII. 3), and the form of these corresponding surfaces, which are everywhere covered with cartilage, is such as to admit of free motion backwards and forwards, that is, of extension and flexion; but to prevent any degree of motion in any other direction. The joint is therefore a hinge-joint, of which the two motions of flexion and extension are the proper motions. This hinge is formed on the part of the humerus by a grooved surface, with lateral projections (fig. LXIX. 2, 3, 4), and on the part of the ulna by a middle projection with lateral depressions (fig. LXIX. 5): the middle projection of the ulna turning readily on the grooved surface of the humerus (fig. LXIX. 2).

160. The bones are held in their proper situation, first, by a ligament on the fore part of the arm, called the anterior (fig. LXXIV. 6), which arises from the lower extremity of the humerus, and is inserted into the upper part of the ulna and the coronary ligament of the radius (fig. LXXIV. 6. 8); secondly, by another ligament on the back part of the arm, called the posterior ligament (fig. LXXV. 8), placed in the cavity of the humerus that receives the olecranon of the ulna (fig. LXXV. 8); and thirdly, by two other ligaments at the sides of the ulna (fig. LXXV. 6, 7). The ulna and radius are united, first, by a ligament called the coronary, which, arising from the ulna, passes completely around the head of the radius (fig. LXXVI. 3), and the attachment of which, while sufficiently close to prevent the separation of the two bones, is yet not adherent to the radius, for a reason immediately to be assigned; secondly, by another ligament which passes in an oblique direction from one bone to the other (fig. LXXVI. 4); and thirdly, by a dense and broad ligament, termed the _interosseous_ (figs. LXXIV. 10, and LXXVI. 5), which fills up the space between the two bones nearly in their whole extent. This ligament serves other offices besides that of forming a bond of union, affording, more especially, a greater extent of surface for the attachment of muscles, and separating the muscles on the anterior from those on the posterior part of the limb.

Anterior view of the ligaments of the elbow-joint. 1. The
lower portion of the humerus; 2. the upper portion of the
radius; 3. the upper portion of the ulna; 4. the internal
condyle; 5. the external condyle; 6. the anterior ligament;
7. portion of the internal lateral ligament; 8. portion of
the coronary ligament; 9. the oblique ligament; 10. upper
portion of the interosseous ligament.]

Posterior view of the ligaments of the elbow-joint. 1. Lower
end of the humerus; 2. internal condyle; 3. external condyle;
4. the olecranon process of the ulna; 5. the upper portion of
the radius; 6. the internal lateral ligament; 7. the external
lateral ligament; 8. the posterior ligament.]

View of the ligaments connecting the ulna and radius at their upper part. 1. The radius; 2. the ulna; 3. the coronary ligament surrounding the head of the radius; 4. the oblique ligament passing from the ulna to the tubercle of the radius; 5 the upper portion of the interosseous ligament.]

161. At their inferior extremities the ulna and radius are united partly by the interosseous ligament (fig. LXXVII. 1) and partly by ligamentous fibres which pass transversely from one bone to the other (fig. LXXVII. 2) on the anterior and the posterior surface of the fore-arm.

1. Interosseous ligament; 2. transverse fibres passing between the radius and ulna, and uniting the two bones; 3. 4. 5. posterior and lateral ligaments of the wrist joint; 6. ligaments uniting the bones of the wrist with one another; 7. 8. ligaments which attach the metacarpal to the carpal bones; 9. transverse ligaments for the attachment of the phalanges of the fingers; 10. lateral ligaments for the attachment of the phalanges of the fingers 11. ligaments of the thumb.]

162. The lower extremity of the radius is also united to the wrist; and the hand being attached to the wrist, the junction of the hand and the fore-arm is effected by the articulation of the wrist with the radius (fig. LXXVII.). The ligaments which connect the bones of the wrist with the radius are bands of exceeding strength (fig. LXXVII. 3).

163. The muscles that act upon the fore-arm are placed upon the arm (fig. LXXVIII.). The joint of the elbow being a hinge-joint, the fore-arm can admit only of two motions, namely, flexion and extension. The muscles by which these motions are effected are four, two for each; the two flexors being placed on the fore part (fig. LXXVIII. 2. 4), and the two extensors on the back part of the arm (fig. LXXIX. 5).

164. The two flexor muscles of the fore-arm are termed the biceps and the brachialis (fig. LXXVIII. 2, 4). The biceps is so called because it has two distinct heads or points of origin (fig. LXXVIII. 2), both of which arise from the scapula (fig. LXXVIII. 2). About a third part down the humerus the two heads meet, unite and form a bulky muscle (fig. LXXVIII. 2), which, when it contracts, may be felt like a firm ball on the fore part of the arm, the upper part of the ball marking the point of union of the two heads (fig. LXXVIII. 2). The muscle gradually becoming smaller, at length terminates in a rounded tendon (fig. LXXVIII. 3), which is implanted into the tubercle of the radius a little below its neck (fig. LXXVIII. 3). It is an exceedingly thick and powerful muscle, and its manifest action is to bend the fore-arm with great strength. But since its tendon is inserted into the radius, besides bending the fore-arm, it assists other muscles that also act upon the radius in the performance of a function to be described immediately (168).

View of the flexor muscles of the fore-arm. 1. The anterior surface of the scapula; 2. the muscle called biceps; 3. tendon of the biceps passing to the tubercle of the radius; 4. the muscle called brachialis.]

165. The second flexor of the fore-arm, termed the brachialis, is placed immediately under the biceps, and is concealed by it for a considerable part of its course (fig. LXXVIII. 4). Arising from the humerus, on each side of the insertion of the deltoid, it continues its attachment to the bone all the way down the fore part of the humerus, to within inch of the joint; it then passes over the joint, adhering firmly to the anterior ligament (fig. LXXVIII. 4), and is inserted by a strong tendon into the ulna (fig. LXXVIII. 4). It is a thick and fleshy muscle, powerfully assisting the action of the biceps.

166. The two extensor muscles are named the triceps and the anconeous (fig. LXXIX.). The triceps, seated on the back part of the arm, derives its name from having three distinct points of origin, or three separate heads (fig. LXXIX. 5); one of which arises from the scapula and two from the humerus (fig. LXXIX. 5). All these heads adhere firmly to the humerus, as the brachialis does on the fore part of the arm, down to within an inch of the joint (fig. LXXIX. 5), where they form a strong tendon, which is implanted into the olecranon of the ulna (fig. LXXIX. 3); the projection of which affords a lever for increasing the action of the muscle. In all animals that leap and bound, this process of the ulna is increased in length in proportion to their power of performing these movements. The triceps forms an exceedingly thick and strong muscle, which envelops the whole of the back part of the arm (fig. LXXIX.); its action is simple and obvious; it powerfully extends the fore-arm. The anconeous, a small muscle of a triangular form, arising from the external condyle of the humerus, and inserted into the ulna a little below the olecranon, assists the action of the triceps.

View of the extensor muscles of the fore-arm. 1. The scapula; 2. the upper part of the humerus; 3. upper end of the ulna; 4. upper end of the radius; 5. the muscle called _triceps_, the extensor of the fore-arm.]

167. Such are the motive powers which act upon the fore-arm, and which produce all the motions of which the hinge-joint of the elbow renders it capable. But besides flexion and extension, the fore-arm is capable of the motion of rotation, which is accomplished by means of the radius. It has been shown (157) that the top of the rounded head of the radius is excavated into a shallow cup (figs. LXIX. 6, and LXXIII. 4) which receives a corresponding convexity of the humerus (figs. LXIX. 2, and LXXIII. 2). In consequence of this articulation with the humerus, the radius, like the ulna, can move backwards and forwards in flexion and extension, the proper movements of the hinge-joint; but that portion of the margin of the hinge of the radius which is in apposition with the ulna is convex (fig. LXIX. 6), and is received into a semilunar cavity hollowed out in the ulna (fig. LXIX. 5). In this cavity the rounded head of the radius revolves, the two bones being held together by the ligament already described (160), which surrounds the head of the radius (fig. LXXVI. 3), and which holds it firmly without being adherent to it, and without impeding in any degree the rotatory motion of the radius. Below, the surface of the radius next the ulna is hollowed out into a semilunar cavity (fig. LXXXII. 1), which receives a corresponding convex surface of the ulna (fig. LXXXII. 2), upon which convex surface the radius rolls (fig. LXXXII. 1). Thus, by the mode in which it is articulated with the ulna above, the radius turns upon its own axis. By the mode in which it is articulated with the ulna below, the radius revolves upon the head of the ulna; and, in consequence of both articulations, is capable of performing the motion of rotation. Moreover, the hand being attached to the radius through the medium of the wrist (figs. LXXXII. 1. 4. and LXXXIII. 1. 4) must necessarily follow every movement of the radius; the rotation of which brings the hand into two opposite positions. In the one, the palm of the hand is directed upwards (fig. LXXXII.); in the other, it is turned downwards (fig. LXXXIII.). When the hand is turned upwards, it is said to be in the state of _supination_ (fig. LXXXII.); when downwards, in that of _pronation_ (fig. LXXXIII.). A distinct apparatus of muscles is provided for effecting the rotation of the radius, in order to bring the hand into these opposite states: one set for producing its supination, and another its pronation.

168. The principal supinators arise from the external condyle of the humerus (fig. LXXX.), and are called long and short (fig. LXXX. 4, 5). The long supinator extends as far as the lower end of the radius, into which it is inserted (fig. LXXX. 4): the short supinator surrounds the upper part of the radius, and is attached to it in this situation (fig. LXXX. 5.). Moreover, the triceps, being inserted into the radius (164), often cooperates with the supinators and powerfully assists their action.

169. The principal pronators are also two, called the round and the square (figs. LXXXI. and LXXXVI. 1). The round pronator arises from the internal condyle, and passing downwards, is inserted into the middle of the radius (fig. LXXXI. 4); the square pronator is a small muscle between the radius and ulna, at their lower extremities being attached to each (fig. LXXXVI. 1).

View of the supinators of the radius and hand. 1. The humerus; 2. the ulna; 3. the radius; 4. the muscle called the long supinator passing to be inserted into the lower portion of the radius; 5. the muscle, called the short supinator, surrounding the upper part of the radius.]

170. The action of these muscles in producing the rotation of the radius, and so rendering the hand supine or prone, is sufficiently manifest from the mere inspection of the diagrams (fig. LXXXI. 4).

View of the pronators of the hand. 1. Lower end of the humerus; 2. the radius; 3. the ulna; 4. the muscle called the round _pronator_, one of the powerful pronators of the hand.]

171. The hand is composed of the carpus, metacarpus, and fingers.

172. The carpus (fig. LXXXII. 4) consists of eight small wedge-shaped bones, placed in a double row, each row containing an equal number, and the whole disposed like stones in an arch (fig. LXXXII. 4). They do in fact form an arch, the convexity of which is upwards, on the dorsal surface (fig. LXXXIII. 4); and the concavity downwards, on the palmar surface (fig. LXXXII. 4). But they differ from the stones of an arch in this, that each bone is joined to its fellow by a distinct moveable joint, each being covered with a smooth articulating cartilage. At the same time all of them are tied together by ligaments of prodigious strength, which cross each other in every direction (fig. LXXVII. 6), so that the several separate joints are consolidated into one great joint. The consequence of this mechanism is that some degree of motion is capable of taking place between the several bones, which, when multiplied together, gives to the two rows of bones such an extent of motion, that when the wrist is bent the arch of the carpus forms a kind of knuckle. By this construction a facility and ease of motion, and a power of accommodation to motion and force, are obtained, such as belong to no arch contrived by human ingenuity.

1. Lower extremity of the radius; 2. lower extremity of the ulna; 3. styloid process of the ulna; 4. bones of the carpus or wrist; 5. metacarpal bones; 6. first phalanges of the fingers; 7. second phalanges of the fingers; 8. third phalanges of the fingers.]

173. The metacarpus (fig. LXXXII. 5), the middle portion of the hand, interposed between the wrist and the fingers, is composed of five bones, which are placed parallel to each other (fig. LXXXII. 5). They are convex outwardly, forming the back (fig. LXXXIII. 5), and concave inwardly, forming the hollow of the hand (fig. LXXXII. 5). They are large at each end, to form the joints by which they are connected with the wrist and fingers (figs. LXXXII. and LXXXIII.): they are small in the middle, in order to afford room for the lodgment and arrangement of the muscles, that move the fingers from side to side (fig. LXXXVI. 2). Their ends, which are joined to the carpus, are connected by nearly plane surfaces (figs. LXXXII. and LXXXIII.): their ends, which support the fingers, are formed into rounded heads, which are received into corresponding cup-shaped cavities, excavated in the top of the first bones of the fingers (fig. LXXXII. 5.). The powerful ligaments that unite these bones pass, both on the dorsal and the palmar surface, from the inferior extremity of the second row of the carpal to the bases of the metacarpal bones (fig. LXXVII, 7, 8). The ligaments are arranged in such a manner as to limit the motions of the joints chiefly to those of flexion and extension, allowing, however, a slight degree of motion from side to side.

174. Each of the fingers is composed of three separate pieces of bone, called phalanges; the thumb has only two (fig. LXXXII. 6, 7, 8): the phalanges are convex outwardly (fig. LXXXII. 6, 7, 8) for increasing their strength, and flattened inwardly (fig. LXXXIII. 6, 7, 8) for the convenience of grasping. The last bones of the fingers, which are small, terminate at their under ends, in a somewhat rounded and rough surface (fig. LXXXIII. 8), on which rests the vascular, pulpy, and nervous substance, constituting the special organ of touch, placed at the points of the fingers, and guarded on the upper surface by the nail (fig. LXXXII. 8).

1. Lower extremity of the radius; 2. lower extremity of the ulna; 3. styloid process of the ulna; 4. bones of the carpus; 5. metacarpal bones; 6. 7. 8. first, second, and third phalanges of the fingers.]

175. The round inferior extremity of the metacarpus is admitted into the cavity of the superior extremity of the first phalanx of the five fingers (figs. LXXXII. and LXXXIII.), and their joints are connected by lateral and transverse ligaments of great strength (fig. LXXVII. 9). The situation and direction of the ligaments which unite the several phalanges of the fingers (fig. LXXVII. 9) are precisely the same as those of the articulation of the phalanges with the metacarpus (fig. LXXVII. 7, 8); and the articulation of these bones with one another is such as to admit only of the motions of flexion and extension.

176. The muscles which perform these motions are seated for the most part on the fore-arm. Independently of the supinators and pronators which have been already described (167 et seq.), there are distinct sets of muscles for bending and extending the wrist and the fingers. The flexors arise from the internal, and the extensors from the external, condyle of the humerus (fig. LXIX. 3, 4). The internal condyle is larger and longer than the external (fig. LXIX. 3, 4); for the flexors require a larger point of origin and a longer fulcrum than the extensor muscles; because to the actions of flexion, such as grasping, bending, pulling, more power is necessary than to the action of extension, which consists merely in the unfolding or the opening of the hand previously to the renewal of the grasp.

177. For the same reason, two muscles are provided for flexing, while only one is provided for extending the fingers. The flexors, bulky, thick, and strong, are placed on the fore part of the fore-arm (fig. LXXXIV.). The first, named the superficial flexor (fig. LXXXIV. 1), about the middle of the arm, divides into four fleshy portions, each of which ends in a slender tendon (fig. LXXXIV. 1). As these tendons approach the fingers they expand (fig. LXXXIV. 1), and when in apposition with the first phalanx, split and form distinct sheaths for the reception of the tendons of the second flexor (fig. LXXXIV. 3). After completing the sheath, the tendons proceed forward along the second phalanx, into the fore part of which they are implanted, and the chief office of this powerful muscle is to bend the second joint of the fingers upon the first, and the first upon the metacarpal bone. Its action is assisted by a second muscle, called the deep or profound flexor (fig. LXXXIV. 2), because it lies beneath the former; or the perforans, because it pierces it. Bulky and fleshy, this second flexor, like the first, about the middle of the arm, divides into four tendons, which, entering the sheaths prepared for them in the former muscle (where the tendons are small and rounded for their easy transmission and play), pass to the root of the third phalanx of the fingers into which they are implanted (fig. LXXXIV. 3).

View of the flexor muscles of the fingers. 1. The superficial flexor, divided and turned aside, to show, 2. the deep flexor; 3. sheaths for the tendons of the deep flexor, formed by the splitting of the tendons of the superficial flexor; 4. the anterior annular ligament, divided and turned aside.]

118. The muscle that extends the fingers, called the common extensor, is placed on the back part of the fore-arm (fig. LXXXV.), about the middle of which it divides into four portions which terminate in so many tendons (fig. LXXXV. 2). When they reach the back of the metacarpal bones, these tendons become broad and flat, and send tendinous expansions to each other, forming a strong tendinous sheath which surrounds the back of the fingers (fig. LXXXV. 2). These tendinous expansions are inserted into the posterior part of the bones of the four fingers (fig. LXXXV. 2); and their office is powerfully to extend all the joints of all the fingers (fig. LXXXV. 2).

179. On both the palmar and dorsal regions of the wrist are placed ligaments for tying down these tendons, and preventing them from starting from their situation during the action of the muscles (figs. LXXXIV. and LXXXV.). On the palmar region an exceedingly strong ligament passes anteriorly to the concave arch of the carpus (fig. LXXXIV. 4) for the purpose of tying down the tendons of the flexor muscles. On the dorsal surface (fig. LXXXV.), a similar ligament, passing in an oblique direction from the styloid process of the radius to the styloid process of the ulna (fig. LXXXV. 3), performs the same office in tying down the tendons of the extensor muscle. Both these ligaments are called annular.

View of the extensor muscles of the fingers. 1. The common extensor, sending (2 2 2 2) tendons to each finger; 3. the posterior annular ligament.]

180. In the palm of the hand are placed additional muscles which assist the flexors of the fingers (fig. LXXXVI. 2), being chiefly useful in enabling the fingers to perform with strength and precision short and quick motions. There are especially four small and rounded muscles (fig. LXXXVI. 2), resembling the earth worm in form and size, and hence called lumbricales; but as their chief use is to assist the fingers in executing short and rapid motions, they have also received the better name of the musculi fidicinales.

1. The muscle called the square pronator; 2. muscles seated in the palm of the hand, by which, chiefly, the fingers execute short and rapid motions.]

181. The thumb, in consequence of the comparative looseness of its ligaments, is capable of a much greater extent of motion than the fingers, and can be applied to any part of each of the fingers, to different parts of the hand, and in direct opposition to the power exerted by the whole of the fingers and hand, in the act of grasping. The muscles which enable it to perform these varied motions, and which act powerfully in almost every thing we do with the hand, form a mass of flesh at the ball of the thumb (fig. LXXXVII. 1), almost entirely surrounding it. The little finger is also provided with a distinct apparatus of muscles (fig. LXXXVII. 2), which surrounds its root, just as those of the thumb surround its ball, in order to keep it firm in opposition to the power of the thumb in the act of grasping, and in various other motions.

1. The mass of muscles forming the ball of the thumb; 2. the mass of muscles forming the ball of the little finger; 3. tendons of one of the flexor muscles of the fingers; 4. sheaths formed by the tendons of the superficial flexor for the reception of the tendons of the deep flexor.]

182. The upper extremity is covered by a tendinous expansion or fascia which envelopes the whole arm, encloses its muscles as in a sheath, and affords them, in their strong actions, "that kind of support which workmen feel in binding their arms with thongs." This fascia likewise descends between many of the muscles, forming strong partitions between them, and affording points of origin to many of their fibres, scarcely less fixed than bone itself.

183. From the whole, it appears, that the first joint of the upper extremities, that of the shoulder, is a ball and socket joint, a joint admitting of motion in every direction; that the second joint, that of the elbow, is partly a hinge-joint, admitting of flexion and extension, and partly a rotation joint, admitting of a turning or rotatory motion; and that the joints of the wrist and of the fingers are likewise hinge-joints, admitting at the same time of some degree of lateral motion. When these various motions are combined, the result is that the hand can apply itself to bodies in almost every direction, in any part of the area described by the arm, when all the joints are moved to their utmost extent. There is thus formed an instrument of considerable strength, capable of a surprising variety and complexity of movements, capable of seizing, holding, pulling, pushing and striking with great power, yet at the same time capable of apprehending the minutest objects, and of guiding them with the utmost gentleness, precision, and accuracy, so that there are few conceptions of the designing mind which cannot be executed by the skilful hand.

184. The lower extremities consist of the thigh, leg, and foot.