Fig. LXXIII.1. The internal condyle of the humerus; 2. the externalcondyle of the humerus; 3. the olecranon process of theulna; 4. the head of the radius.
1. The internal condyle of the humerus; 2. the externalcondyle of the humerus; 3. the olecranon process of theulna; 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 orolecranon(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 thehumerus (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 completelyaround 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 theinterosseous(figs. LXXIV. 10, and LXXVI. 5), which fills up the space between the two bones nearly intheir 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.
Fig. LXXIV.Anterior view of the ligaments of the elbow-joint. 1. Thelower portion of the humerus; 2. the upper portion of theradius; 3. the upper portion of the ulna;4. the internal condyle; 5. the external condyle; 6. the anteriorligament; 7. portion of the internal lateral ligament;8. portion of the coronary ligament; 9. the oblique ligament;10. upper portion of the interosseous ligament.
Anterior view of the ligaments of the elbow-joint. 1. Thelower portion of the humerus; 2. the upper portion of theradius; 3. the upper portion of the ulna;4. the internal condyle; 5. the external condyle; 6. the anteriorligament; 7. portion of the internal lateral ligament;8. portion of the coronary ligament; 9. the oblique ligament;10. upper portion of the interosseous ligament.
Fig. LXXV.Posterior view of the ligaments of the elbow-joint.1. Lower end of the humerus; 2. internal condyle; 3. externalcondyle; 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 posteriorligament.
Posterior view of the ligaments of the elbow-joint.1. Lower end of the humerus; 2. internal condyle; 3. externalcondyle; 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 posteriorligament.
Fig. LXXVI.View of the ligaments connecting the ulna and radius attheir upper part. 1. The radius; 2. the ulna; 3. the coronaryligament surrounding the head of the radius; 4. theoblique ligament passing from the ulna to the tubercle ofthe radius; 5 the upper portion of the interosseous ligament.
View of the ligaments connecting the ulna and radius attheir upper part. 1. The radius; 2. the ulna; 3. the coronaryligament surrounding the head of the radius; 4. theoblique ligament passing from the ulna to the tubercle ofthe 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.
Fig. LXXVII.1. Interosseous ligament; 2. transverse fibres passingbetween 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 thecarpal bones; 9. transverse ligaments for the attachmentof the phalanges of the fingers; 10. lateral ligaments forthe attachment of the phalanges of the fingers 11. ligamentsof the thumb.
1. Interosseous ligament; 2. transverse fibres passingbetween 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 thecarpal bones; 9. transverse ligaments for the attachmentof the phalanges of the fingers; 10. lateral ligaments forthe attachment of the phalanges of the fingers 11. ligamentsof 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 whichconnect 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).
Fig. LXXVIII.View of the flexor muscles of the fore-arm. 1. The anteriorsurface 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.
View of the flexor muscles of the fore-arm. 1. The anteriorsurface 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.
Fig. LXXIX.View of the extensor muscles of the fore-arm. 1. Thescapula; 2. the upper part of the humerus; 3. upper endof the ulna; 4. upper end of the radius; 5. the musclecalledtriceps, the extensor of the fore-arm.
View of the extensor muscles of the fore-arm. 1. Thescapula; 2. the upper part of the humerus; 3. upper endof the ulna; 4. upper end of the radius; 5. the musclecalledtriceps, 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 ligamentalready 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 ofsupination(fig. LXXXII.); when downwards, in that ofpronation(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).
Fig. LXXX.View of the supinators of the radius and hand. 1. Thehumerus; 2. the ulna; 3. the radius; 4. the muscle calledthe long supinator passing to be inserted into the lower portionof the radius; 5. the muscle, called the short supinator,surrounding the upper part of the radius.
View of the supinators of the radius and hand. 1. Thehumerus; 2. the ulna; 3. the radius; 4. the muscle calledthe long supinator passing to be inserted into the lower portionof 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).
Fig. LXXXI.View of the pronators of the hand. 1. Lower end of thehumerus; 2. the radius; 3. the ulna; 4. the muscle calledthe roundpronator, one of the powerful pronators of the hand.
View of the pronators of the hand. 1. Lower end of thehumerus; 2. the radius; 3. the ulna; 4. the muscle calledthe roundpronator, 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.
Fig. LXXXII1. Lower extremity of the radius; 2. lower extremity ofthe ulna; 3. styloid process of the ulna; 4. bones of thecarpus or wrist; 5. metacarpal bones; 6. first phalangesof the fingers; 7. second phalanges of the fingers; 8. thirdphalanges of the fingers.
1. Lower extremity of the radius; 2. lower extremity ofthe ulna; 3. styloid process of the ulna; 4. bones of thecarpus or wrist; 5. metacarpal bones; 6. first phalangesof the fingers; 7. second phalanges of the fingers; 8. thirdphalanges 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 themuscles, 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).
Fig. LXXXIII.1. Lower extremity of the radius; 2. lower extremity ofthe ulna; 3. styloid process of the ulna; 4. bones of thecarpus; 5. metacarpal bones; 6. 7. 8. first, second, andthird phalanges of the fingers.
1. Lower extremity of the radius; 2. lower extremity ofthe ulna; 3. styloid process of the ulna; 4. bones of thecarpus; 5. metacarpal bones; 6. 7. 8. first, second, andthird 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 providedfor 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).
Fig. LXXXIV.View of the flexor muscles of the fingers. 1. The superficialflexor, divided and turned aside, to show, 2. the deepflexor; 3. sheaths for the tendons of the deep flexor,formed by the splitting of the tendons of the superficialflexor; 4. the anterior annular ligament, divided and turnedaside.
View of the flexor muscles of the fingers. 1. The superficialflexor, divided and turned aside, to show, 2. the deepflexor; 3. sheaths for the tendons of the deep flexor,formed by the splitting of the tendons of the superficialflexor; 4. the anterior annular ligament, divided and turnedaside.
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.
Fig. LXXXV.View of the extensor muscles of the fingers. 1. Thecommon extensor, sending (2 2 2 2) tendons to eachfinger; 3. the posterior annular ligament.
View of the extensor muscles of the fingers. 1. Thecommon extensor, sending (2 2 2 2) tendons to eachfinger; 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.
Fig. LXXXVI.1. The muscle called the square pronator; 2. musclesseated in the palm of the hand, by which, chiefly, thefingers execute short and rapid motions.
1. The muscle called the square pronator; 2. musclesseated in the palm of the hand, by which, chiefly, thefingers 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.
Fig. LXXXVII.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 flexorfor the reception of the tendons of the deep flexor.
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 flexorfor 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.
185. The osseous part of the thigh consists of a single bone, called the femur (fig. XXXIV. 4), the longest, thickest, and strongest bone in the body. It sustains the entire weight of the trunk, and occasionally much heavier loads superimposed upon it. It is constructed in such a manner as to combine strength with lightness. This is effected by rendering the bone what is technicallycalled cylindrical; that is, a bone in which the osseous fibres are arranged around a hollow cylinder. There are two varieties of osseous matter,—the compact, in which the fibres are dense and solid (fig. LXXXVIII. 1), and the spongy, in which the fibres are comparatively tender and delicate (fig. LXXXVIII. 2). Both varieties are, indeed, combined, more or less, in every bone, the compact substance being always external, and the spongy internal; but in the cylindrical bones the arrangement is peculiar. Every long or cylindrical bone consists of a body or shaft (fig. LXXXVIII. 4.), and of two extremities (fig. LXXXVIII. 5). The body is composed principally of compact substance, which on the external surface is so dense and solid, that scarcely any distinct arrangement is visible; but towards the interior this density diminishes; the fibres become distinct (fig. LXXXVIII. 5), and form an expanded tissue of a cellular appearance (fig. LXXXVIII. 5), the cells being called cancelli, and the structure cancellated. In the centre of the bone even the cancelli disappear; the osseous fibres terminate; and a hollow space is left filled up, in the natural state, by an infinite number of minute membranous bags which contain the marrow (fig. LXXXVIII. 3). In the body of the bone, to which strength is requisite, that part being the most exposed to external violence, the compact matter is arranged around a central cavity. By this means strength is securedwithout any addition of weight; for the resisting power of a cylindrical body increases in proportion to its diameter; consequently the same number of osseous fibres placed around the circumference of a circle produce a stronger bone than could have been constructed had the fibres been consolidated in the centre, and had the diameter been proportionally diminished. The hollow space thus gained in its centre, renders the bone lighter by the subtraction of the weight of as many fibres as would have gone to fill up that space; while its strength is not only not diminished by this arrangement, but positively increased. On the other hand, at the extremities of the bone, space, not strength, is required; required for the attachment and arrangement of the tendons of the muscles that act upon it, and for the formation of joints (fig. LXXXVIII. 5). Accordingly, at its extremities the bone swells out into bulky surfaces; but these surfaces are composed, not of dense and solid substance, but of spongy tissue, covered by an exceedingly thin crust of compact matter, and so, as by the former expedient strength is secured without increase of weight, by this, space is obtained without increase of weight.
Fig. LXXXVIII.A section of the femur, showing, 1. the compact bonysubstance; 2. the spongy or cancellated structure; 3. theinternal cavity containing the marrow; 4. body; 5, extremitiesof the bone.
A section of the femur, showing, 1. the compact bonysubstance; 2. the spongy or cancellated structure; 3. theinternal cavity containing the marrow; 4. body; 5, extremitiesof the bone.
186. The thigh-bone, placed at the under and outer part of the pelvis, has an oblique direction, the under being considerably nearer its fellow than the upper end (fig. XXXIV. 4), in order to afford space for the passages at the bottom of the pelvis, and also to favour the action of walking. The body of the bone, which is of a rounded form (fig. XXXIV. 4), is smooth on its anterior surface (fig. XXXIV. 4), where it is always slightly convex, the convexity being forwards (fig. XXXIV. 4), while its posterior surface is irregular and rough, and forms a sharp prominent line, termed the linea aspera (fig. XXXV. 4), giving attachment to numerous muscles.
187. The superior extremity of the femur terminates in a large ball or head, which forms nearly two-thirds of a sphere (fig. LXXXIX. 4.). It is smooth, covered with cartilage, and received into the socket of the ilium called the acetabulum, which, deep as it is, is still further deepened by the cartilage which borders the brim (fig. LXXXIX. 3). The brim is particularly high in the upper and outer part, because it is in this direction that the reaction of the ground against the descending weight of the trunk tends to dislodge the ball from its socket.
188. Passing obliquely downwards and outwards from the ball, is that part of the femur which is called the neck (fig. LXXXIX. 5). It spreads out archlike between the head and the body of the bone, and is more than an inch in length (fig. LXXXIX. 5). It is thus long in order that the head of the bone may be set deep in its socket, and that its motions may be wide, free, and unembarrassed.
Fig. LXXXIX.1. Lower portion of the ilium; 2. tuberosity of theischium: 3. socket for the head of the femur, or thigh-bone;4. head of the femur; 5. neck of the femur; 6. thegreat process of the femur called the trochanter major;7. the body of the femur.
1. Lower portion of the ilium; 2. tuberosity of theischium: 3. socket for the head of the femur, or thigh-bone;4. head of the femur; 5. neck of the femur; 6. thegreat process of the femur called the trochanter major;7. the body of the femur.
189. From the external surface of the femur, nearly in a line with its axis, proceeds the largest and strongest bony process of the body which gives insertion to its most powerful muscles, namely, those that extend the thigh and that turn it upon its axis (fig. LXXXIX. 6). Because, from its oblique direction, it rotates the thigh, this process is called the trochanter, and, from its size, the trochanter major. At the under and inner part of the neck on the posterior surface of the bone, is a similar process, but much smaller, called the trochanter minor (fig. XXXV. 4), into which are inserted the muscles that bend the thigh.
190. The inferior extremity of the femur, much broader and thicker than the superior (fig. XC. 1), is terminated by two eminences, with smooth surfaces, termed condyles (fig. XC. 2), which, articulated with the tibia, and the patella, form the joint of the knee (figs. XC. 2, 4, 5, and XCI. 1, 2, 3).
Fig. XC.1. Lower end of the femur; 2. condyles of the femur;3. upper end of the tibia; 4. articular surfaces on the headof the tibia on which the thigh-bone plays; 5. the patella,or knee-pan; 6. upper end of the fibula, not entering intothe knee-joint.
1. Lower end of the femur; 2. condyles of the femur;3. upper end of the tibia; 4. articular surfaces on the headof the tibia on which the thigh-bone plays; 5. the patella,or knee-pan; 6. upper end of the fibula, not entering intothe knee-joint.
Fig. XCI.Posterior view of the bones forming the knee-joint.1. Lower end of the femur; 2. upper end of the tibia;3. articular surfaces on the head of the tibia, on whichthe thigh-bone plays; 4. upper end of the fibula, not enteringinto the knee joint.
Posterior view of the bones forming the knee-joint.1. Lower end of the femur; 2. upper end of the tibia;3. articular surfaces on the head of the tibia, on whichthe thigh-bone plays; 4. upper end of the fibula, not enteringinto the knee joint.
191. The bones of the leg, two in number, consist of the tibia (fig. XC. 3) and fibula (fig. XC. 6). The tibia, next to the femur, the longest bone in the body, is situated at the inner side of the leg (fig. XC. 3). Its superior extremity is bulky and thick (fig. XC. 3). The top of it forms two smooth and slightly concave surfaces, adapted to the convex surfaces of the condyles of the femur (fig. XC. 4, 2). On its outer side there is a smooth surface, to which the head of the fibula is attached (fig. XC. 6). Its lower extremity, which is small, forms a concavity adapted to the convexity of the bone of the tarsus, called the astragalus, with which it is articulated (fig. XCII. 4.) Its inner part is produced so as to form the inner ankle (figs. XCII. 2, and XCIII. 3): its outer side is excavated into a semilunar cavity, for receiving the under end of the fibula, which forms the outer ankle (figs. XCII. 3, and XCIII. 4).
192. The fibula, in proportion to its length the most slender bone of the body, is situated at the outer side of the tibia (fig. XC. 6). Its upper end formed into a head, with a flat surface on its inner side (figs. XC. 6, and XCI. 4), is firmly united to the tibia (fig. XC. 4). Its lower end forms the outer ankle, which is lower and farther back than the inner (fig. XCII. 3, 2).
Fig. XCII.Anterior view of the bones forming the ankle-joint.1. Lower end of the tibia; 2. production of the tibia, formingthe inner ankle; 3. lower end of the fibula, forming theouter ankle; 4. upper part of the astragalus: these threebones form the ankle-joint; 5 5 5, other bones of the tarsus;6 6 6 6 6 metatarsal bones.
Anterior view of the bones forming the ankle-joint.1. Lower end of the tibia; 2. production of the tibia, formingthe inner ankle; 3. lower end of the fibula, forming theouter ankle; 4. upper part of the astragalus: these threebones form the ankle-joint; 5 5 5, other bones of the tarsus;6 6 6 6 6 metatarsal bones.
Fig. XCIII.Posterior view of the bones forming the ankle-joint.1. Lower end of the tibia; 2. lower end of the fibula; 3. internalmalleolus or ankle; 4. external malleolus or ankle;5. one of the tarsal bones, called the astragalus, with whichthe tibia and fibula are articulated; 6. the os calcis or heel.
Posterior view of the bones forming the ankle-joint.1. Lower end of the tibia; 2. lower end of the fibula; 3. internalmalleolus or ankle; 4. external malleolus or ankle;5. one of the tarsal bones, called the astragalus, with whichthe tibia and fibula are articulated; 6. the os calcis or heel.
193. The patella, or knee-pan (fig. XC. 5), is a light but strong bone, of the figure of the heart as painted on playing-cards, placed at the fore part of the joint of the knee, and attached by a strong ligament to the tibia, the motions of which it follows (fig. XC. 5). It is lodged, when the knee is extended, in a cavity formed for it in the femur (fig. XC.); when bent, in a cavity formed for it at the fore part of the knee (fig. XC. 5).
194. The foot consists of the tarsus, metatarsus, and toes.
195. The tarsus, or instep, is composed of seven strong, irregular-shaped bones, disposed like those of the carpus, in a double row (fig. XCII. 4, 5). The arrangement of the tarsal bones is such as to form an arch, the convexity of which above, constitutes the upper surface of the instep (fig. XCII. 4, 5): in the concavity below are lodged the muscles, vessels, and nerves that belong to the sole.
196. The metatarsus consists of five bones, which are placed parallel to each other (fig. XCII. 6), and which extend between the tarsus and the proper bones of the toes (fig. XCII. 6). Their extremities, especially next the tarsus, are large, in order that they may form secure articulations with the tarsal bones (fig. XCII. 6). Their bodies are arched upwards (fig. XCII. 6), slightly concave below, and terminate forwards in small, neat, round heads, which receive the first bones of the toes, and with which they form joints, admitting of a much greater degree of rotation than is ever actually exercised, in consequence of the practice of wearing shoes. The natural, free, wide-spreading form of the toes, and the consequent security with which they grasp the ground, is greatly impaired by this custom. Taken together, the bones of the metatarsus form a second arch corresponding to that of the tarsus (fig. XCVIII. 2).
197. Each toe consists of three distinct bones,called, like those of the fingers, phalanges (fig. XCVIII.), but the great toe, like the thumb, has only two (fig. XCVIII.). That extremity of the first phalanges which is next the metatarsal bones is hollowed into a socket for the head of the metatarsal bones.
198. Besides the bones already described, there are other small bones, of the size and figure of flattened peas, found in certain parts of the extremities, never in the trunk, called sesamoid, from their resemblance to the seed of the sesamum. They belong rather to the tendons of the muscles than to the bones of the skeleton. They are embedded within the substance of tendons, are found especially at the roots of the thumb and of the great toe, and are always placed in the direction of flexion. Their office, like that of the patella, which is, in truth, a bone of this class, is to increase the power of the flexor muscles by altering the line of their direction, that is, by removing them farther from the axis of the bone on which they are intended to act.
199. The ligaments which connect the bones of the lower extremities are the firmest and strongest in the body. Of these, the fibrous capsule of the hip-joint (fig. XCIV. 1), which secures the head of the femur in the cavity of the acetabulum (fig. XCIV.), is the thickest and strongest. It completely surrounds the joint (fig. XCIV. 1). It arises from the whole circumference of the acetabulum,and, proceeding in a direction outwards and backwards, is attached below to the neck of the femur (fig. XCIV. 1). It is thicker, stronger, and much more closely attached to the bones than the fibrous capsule of the shoulder-joint (144), because the hip-joint is formed, not like the shoulder-joint, for extent of motion, but for strength. Its internal surface is lined by synovial membrane, and its external surface is covered and strengthened by the insertion of muscles that move the thigh-bone. The joint is strengthened by another ligament, which passes from the inner and fore part of the cavity of the acetabulum (fig. XCV.) to be inserted into the head of the femur (fig. XCIV.), called the round ligament, the office of which obviously is to hold the head of the femur firmly in its socket.