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CONTRIBUTIONS TO THE STUDY OF SOME AFRICAN MAMMALS 259 Contributions to the study of some African Mammals.-111. Adaptations in the bones of the fore-limb of the Lion, Leopard, and Cheetah. By A. TIND~LI, HOPWOOD, DSc., F.L.S., Department of Geology, British Museum (Natural History). (With 6 Text-figures) [Read 7 June 19451 After spending some time on the study of the limb-bones of highly specialized cursorial animals such as the antelopes (Hopwood, 1936), it seemed desirable to extend one’s observations to a more generalized kind. For this purpose the forelimbs of the three big cats of the African fauna were selected because they offer the greatest variety within a single family. Generally speaking, the Lion lives either in sandy or semi-desert places where there is plenty of scrub in which to hide, or else in rank vegetation bordering water. It is not given to climbing trees, although it may scramble up a sloping trunk, and is never found far inside forests. Over short distances it can move as fast as a horse in a shuffling, shambling gallop, but its usual gait is a somewhat deliberate walk. The Leopard, on the other hand, lives in wooded country and climbs trees with ease. In areas where forests are absent, it lives in broken, rocky, scrub-coveredplaces. As a rule it does not travel so far from its lair as does the Lion, neither is its greatest speed equal to t h t of the Lion. The Cheetah is never met with away from the open plains ; it obtains its prey by running it down, and over short distances of a few hundred yards is the swiftest of all mammals. These differences in habit should be reflected in the skeleton of the limbs, especially in that of the fore-limb which is much more characteristic than that of the hind-limb. All the skeletons were obtained in the neighbourhood of Olduvai, on the eastern edge of the Serengeti plains, and are preserved in the Department of Zoology of the British Museum. Most of them were collected by Capt. J. R. H. Hewlett during Dr.Leakey’s expedition of 1931. The scapulae of the Leopard and Cheetah are of about the same size, &q.ru.h. but that of the Cheetah is narrower, has a wider and shallower supraacapular notch, and a straighter anterior border. The spine overhangs the infkpinous fossa to a greater extent carrying the insertions of the trapezius and the origin of the deltoid farther back, and closer to the trunk, than they are in the Leopard. On the inner, or medial, surface of the bone the scar for the serratus magnus and levator anguli scapulae is placed almost entirely behind the spine ; it forms a rectangle which is deeper dorso-ventrally than it is wide. In the Leopard, on the other hand, this scar extends right across the position of the spine, and forms a diamond-shaped figure which is much wider antero-posteriorlythan it is deep dorso-ventrally. Finally, the upper end ofthe axillary border has a pronounced inward curvature in the Cheetah, whereas in the Leopard the curvature is slight ; consequently, the insertions of the serratus magnus and rhomboideus major are nearer to the sagittal plane of the body of the Cheetah than they are to that of the Leopard. As a whole, the scapula of the Lion resembles that of the Leopard rather than that of the Cheetah, but it agrees with that of the latter in having a rather straighter anterior border and a shallower, wider, suprascapular notch. The insertion of the spine to the body of the scapula is more oblique than it is in the Leopard, but not so oblique as in the Cheetah. On the inner surface the general shape and position of the insertions of the serratus magnus and levator anguli scapulae are much the same as those of the Leopard, but in the increased dorso-ventral depth an approach is made JOU&X. L l X N . SOC, -!400&0QY,VOL. XLI. 19 260 DR. A . TINDELL HOPWOOD ON to a Cheetah-like condition. The broad and massive metacroniian processes of the Lion and Cheetah are in marked cont'rast, to the Leopard's relatively slender hook ; the origins of the levator claviculae and part of the spinous head of the deltoid are attached to this process. The acromion process is much stouter in the Lion than it is in either of the other species, from it the acromial portion of the deltoid takes its origin. Of these three bones, that of the Leopard is the most generalized. The greater width, the more erect spine, the more diffuse and less concentrated muscle attachments, all of these facilitate a greater mobility of the shoulder. In the Lion, the rather more oblique spine limits the action of the trapezius and forces it to work more in one plane ; at the same time, by taking t,he origin of the deltoid closer to the body, it limits the abductor function of the muscle. The serratus magnus and levator angdi scapulae are responsible for the backwards and forwards motion of the scapula and their efficiency increases with the dorso-ventral depth of their insertions. They also raise the thorax, and the eficiency of this movement depends on the antero-posterior width of the insertion. Evidently, therefore, movement to and fro is more important FIG. 1.-Diagram of the upper part of the medial surface of the scapula to show the Mering shape of the area of insertion of the mm. serratus magnus et levator anguli scapulae in the Leopard (dotted),Lion (continuous),and Cheetah (heavy). Not to scale. to the Cheetah, because it directly affects the speed of the animal, whereas in the Leopard most stress is laid upon raising the thorax, which is important in climbing. The scapula of the Lion is intermediate in type ; the speed of its gallop is reflected in the shape of the muscle scars, and the need for a relatively mobile shoulder is to be seen in those points in which it resembles the Leopard rather than the Cheetah. Huwrus. The humeri of the Lion and the Cheetah differ from that of the Leopard in contrasting ways ; that of the Lion, as befits so large and powerful an animal,.is more massive, whereas that of the Cheetah is laterally compressed and more slender. In consequence of the lateral compression, the greater tuberosity of the Cheetah is more nearly parallel to the sagittal plane of the humerus than it is in either of the other two species ; it is also taller, and the insertion of the infraspinatus is above the level of the head of the humerus, whereas, in the Lion and the Leopard this insertion is at the same level as the head. Viewed from above, the insertions of the supraspinatus to the greater, and of the subscapularisto the lesser tuberosity are visible. Because of the lateral compression, the insertion of the supraspinatus forms a smaller angle to the sagittal plane of the head in the Cheetah than it does in the other two species ; 15" to 20" as compared CONTRIBUTIONS TO THE STUDY OF SOME AFRICAN MAMMALS 261 with 30" in the Lion and Leopard. But if the Lion agrees with the Leopard in this respect, it approaches the Cheetah rather than the Leopard in the manner of the insertion of the subscapularis. In all three species this insertion passes backwards and downwards, but, whereas in the Leopard only the anterior one-third of the insertion faces upwards and the remainder inwards towards the trunk, half the scar faces upwards in the Lion and the remainder is not so markedly inward facing. I n the Cheetah the scar faces inwards hardly a t all, and the chief feature on the medial aspect is the sharp angle which forms the proximal margin of the tuberosity. The chief features on the shaft are the humeral crest and deltoid tuberosity, the linea tuberculi majoris, and the teres tubercle ; all of these vary in position according to the species. The insertion of the teres minor is about equidistant between the anterior and posterior margins of the bone in the Cheetah ; even in the adult male the deltoid tuberosity is very small and indistinct whereas the backwards-facing tubercle for the insertion of the teres minor is prominent. In the Leopard the insertion of the teres minor forms a relatively large, pyramidal tubercle, which is much more distinct than the insertion of the deltoid and is nearer the posterior than it is t o the anterior margin of the bone. The deltoid tuberosity is approximately equidistant between the anterior and posterior margins of the lateral surface of the shaft, on which it forms a sharp ridge. Conditions in the Lion are t o some extent intermediate between those in the other two species. The insertion of the teres minor is distinct but generalized ; the deltoid tuberosity is less than one-third of the width of the shaft from the anterior margin, and is stronger than it is in either of the other species. The insertion of the teres minor is intermediate in position between that of the Leopard and the Cheetah. The most important feature on the medial aspect of the shaft is the teres tubercle. Its variation may be most easily estimated by imagining a line drawn across the shaft so as t o mark off the proximal third. If this be done, then the lower end of the teres tubercle of the Leopard touches the line, that of the Lion is below the line, and that of the Cheetah is well above it. Sometimes the teres tubercle of the Leopard approximates in position t o that of the Lion, though it is never quite so low, but it appears to be an invariable rule that in all three species the centre of the tubercle is directly opposite t o that of the deltoid tuberosity. Both the Lion and the Leopard have the humeral crest and the linea tuberculi majoris widely separated as far as the deltoid tuberosity, below which the humeral crest turns more or less sharply to meet the linea tuberculi majoris. The humeral crest of the Cheetah does not change its direction at the deltoid tuberosity, but continues in an even sweep throughout its course. The medial epicondyle, t o which the flexor inuscles of the hand are attached, is large and salient in the Lion and Leopard, but forms a low dome in the Cheetah. Both the Lion and the 1,eopard display a linear arrangement of the muscle attachments t o the epicondyle, hiit whereas in the Lion this line forms an angle of about 45" with the inferior margin of the trochlea, the corresponding angle in the Leopard is about 75" bringing the line of attachments more nearly parallel t o the length of the shaft. In the Cheetah the scars have a crescentic arrangement, with the concavity facing upwards and backwards. The differences between the lateral epicondyles of the three species are slight and inconstant. There do not appear t o be any outstanding differences between the distal articular surfaces of the humeri of the Lion and Leopard, but the margins of the trochlea, both lateral and medial, are more nearly parallel t o the sagittal plane of the shaft in the Cheetah than they are in the other two species. The muscles of the shoulder and arm are best considered under the well-known heads of extensors and flexors ; some of them have other functions as well, but for our present purpose those functions are of secondary importance. The most important extensor is the supraspinatus which is reinforced by the sub-scapularis and, depending on the position of the head of the humerus in the glenoid cavity of the scapula, by 19 * 262 DE. A. TINDPLL POPWOOD ON FIG.2.-Superimposed outlines of the humerus, radius and ulna. of Leopard (shadedand dotted)* Lion (continuous),and Cheetah (heavy). The vertical distance between the horizontal lines ia 8 common length to which all the outlines were reduced in order to make the relative proportions visible at a glance. CONTRIBUTIONS TO THE STUDY OF SOME AFRICAN MAMMALS 263 the infra-spinatus, both of them exercising secondary functions. The flexor group is made up of the deltoid, the latissimus dorsi, the teres major and the teres minor. According t o the position of the head of the humerus, they may be reinforced by the infraspinatus . This contrast in number and mass of the two groups of muscles is, of course, a reflection of the difference between advancing the fore-limb and restoring it t o its normal position beneath the trunk. When moving, the animal &st flexes the forelimb t o raise it from the ground and then extends it ; in so doing the energy used is that required t o overcome the inertia of the limb. Once the limb touches the ground it is fixed and the body-weight has t o be moved forward t o it. This weight is moved partly by the push of the hind-limb, and partly by the pull of the fore-limbs. The pull is largely provided by the latissimus dorsi and pectoralis profundus, which draw the body up t o the limb, but it is supplemented by the action of the muscles which flex the shoulder as the body moves forward. This more or less passive drag exercised by the flexor group is in contrast t o the active pull of the latissimus dorsi and pectoralis profundus, nevertheless, it is important because the total mass of the flexores is, t o some extent, determined by the proportion of the inertia of the trunk which they overcome in flexing the limb. From these general considerations we may pass on t o consider in some detail the action ofthe more important muscles inserted t o the humerus, and t o notice how the manner of their insertion and the amount of the lateral compression of the humerus affect the movement of the bone. The relative amount of lateral compression may be estimated by comparing the medio-lateral diameter a t the level ofthe deltoid tuberosity with the antero-posterior diameter a t the same level. Approximate values are, Leopard 75%, Lion 70%, Cheetah 57%. The reduction of the transverse diameter of the humerus reduces the mechanical advantage of the abductor muscles, and limits the sideways motion of the limb. Taken in the order in which they.are mentioned in the description of the bones, the principal muscles inserted t o the humerus, and their functions, we : infraspinatus, inserts to the lateral surface of the greater tuberosity ; abducts and rotates the arm. According to the position of the caput humeri within the glenoid cavity of the scapula, the muscle may act aa a flexor or aa an extensor. supraspinatus, inserts mainly t o the medial surface of the greater tuberosity ; extends the shoulder joint. subsmpularis, inserts t o the lesser tuberosity ; extends the shoulder joint, advances and adducts the arm. deltoid, inserts t o the deltoid tuberosity ; flexes the shoulder joint and abducts the arm. term minor, inserts to the proximal portion of the humeral crest between the insertion of the infraspinatus and the origin of the anconaeus externus ; flexes the shoulder joint and abducts the arm. latissimus dorsi, inserted t o the teres tubercle in common with the teres major ; flexes the shoulder joint and moves the humerus upwards and backwards. If the limb is fixed in an advanced position, it draws the trunk forward. teres major, inserts t o the teres tubercle in common with the latissimus domi ; flexes the shoulder joint, retracts and adducts the arm. pectoralis profundw, inserts t o the lesser tuberosity ; retracts and adducts the arm. Since the insertion of the infraspinatus of the Cheetah is more nearly parallel to the sagittal plane than it is in either of the other species, the rotatory function of the muscle is lessened, and the position of the insertion relative t o the caput humeri has the further effect of diminishing the abductor function. A similar limitation in the 264 b R . A. TINDELL HOPWOOD ON movement of the limb of the Cheetah is indicated by the insertion of the supraspinatus. Not only does its insertion t o the greater tuberosity make a smaller angle to the sagittal plane of the head of the humerus than in either the Leopard or the Lion, but it is more concentrated towards the anterior margin of the tuberosity. Hence the extensor function of this muscle is emphasized in the Cheetah, and there is less possibility of a lateral excursus as the limb moves too and fro. In the characters of the insertion of the subscapularis and pectoralis profundus muscles, the Lion is clearly intermediate between the Leopard and the Cheetah ; it is evident that, whereas the former lays most stress on the adductor function as being of great iniportance t o a climbing animal, and the latter on the extension of the shoulder and forward movement of the arm, to the Lion both functions are of equal value. As a general rule, the greater the variety of movement of which a limb is capable, the less well defined are the insertions of muscles which perform more than one function. If, however, one function is exercised more than another, then the preponderance of that function is made evident in the character of the muscle scar. This is illustrated by the insertion of the teres minor, which forms a distinct tubercle in the Cheetah, but which is more or less diffuse in the Lion. Having regard to the double function of the muscle, and the mobility of the fore-limb of the Leopard, one might expect that the insertion would be diffuse in that species also, but the muscle is in fact inserted t o a relatively large pyramidal tubercle. In the Cheetah the muscle scar is roughened and faces backwards, and its peculiar tubercle has evidently arisen from the need t o provide a sufficiently large insertion for a powerful flexor muscle working entirely in one plane. In the Leopard the abductor function comes into play, causing the tubercle to be produced laterally and to form a definite pyramid. Neither flexion nor abduction has the pre-eminence in the Lion, consequently the insertion remains in the more primitive. diffuse state. This study of the insertions of tho teres -or is apt to be misleading for it implies that abduction ofthe fore-limb is more important to the Leopard than it is t o the Lion. But when the insertion of the deltoid, which is primarily an abductor muscle, is considered, the position appears to be reversed, for the deltoid tuberosity of the Lion is stouter than that of the Leopard. In the sum, therefore, it is not the function itself, but the point a t which the forces which exercise the function are applied t o the humerus which is variable. That point is nearer the proximal end of the bone in the Leopard than it is in the Lion. The deltoid tuberosity of the Cheetah is not much more than a barely perceptible thickening of the deltoid ridge. By its lack of development, it confirms the relative unimportance of the abductor function of the muscle in this genus. All three species have a teres tubercle of about the same relative strength. This is in accordance with expectation, because the functions of the latiasimus dorsi and teres major are of absolute importance, irrespective of the type of adaption of the limb. Radius. The radius of the Cheetah is slender, graceful, and relatively straight, whereas that of the Lion is stout, rugged, and strongly curved. The radius of the Leopard most nearly resembles that of the Lion in its general character and surfaco markings, but the curvature is less. The insertlion of the long collateral ligament of the elbow is ntarkcd by a pronounced tubercle in the Lion and the Leopard but despite the greater size of the boiie this tubercle is not so prominent in the Cheetah as in the Leopard. Old male Lions have the shorter ligament also inserted t o a tubercle which is immediately below the head of the radius, but in the other two species, and in younger, though fully grown lions-as indicated by complete fusion of the epiphyses with the shaft, the place of insertion of this ligament is hardly t o be discerned. The prominent, ovate, tubercle for the insertion of the biceps is subject to a certain amount of individual variation but in the Cheetah it is nearer to the head of the OONTFUBUTIONS TO THE STUDY OF SOME AFRICAN m s 265 radius and more on the volar surface of the shaft than it is in either of the other species. The latter are also alike in the oblique line which arises from the lower third of the medial margin of the tubercle and passes downwards and inwards to the medial border of the bone, whereas in the Cheetah the same line takes it0 origin from the distal end of the medial margin of the tubercle and by following a less oblique course finally joins the medial margin of the bone well below the insertion of the pronator teres. In the Lion and Leopard the corresponding junction is effected at a point rather more than half-way between the head and the insertion of the pronator teres. The course of the oblique line is partly conditioned by the width of the bone, which is relatively greatest in the Lion and lea& in the Cheetah ; the greater the angle the oblique line makes with the long axis of the radius, the greater the breadth of the flexor profundus digitorum to which it gives origin, and the stronger that muscle is likely to be. The lateral border of the radius is flattened in the Lion and the Leopard, whereas the medial border is relatively sharp ; consequently the cross-section of the shaft of the radius is more or less triangular, but in the Cheetah it is irregularly oval, the curvature being greater on the dorsal surface than it is on the volar. In the two former species the rough line for the interosseous ligament is on the volar edge of the flattened lateral border, but in the Cheetah it is entirely on the volar surface : there, at the centre of tKe shaft, it limits the lateral third of that surface, but it approaches the lateral margin of the bone at either end. The position of the supinator brevis on the upper part of the dorsal surface of the clhaft is marked by a very distinct flattening both in the Lion and in the Leopard, but in the Cheetah this same facet is scarely to be detected. The differences in the insertion of the pronator teres are similar. In the Cheetah the insertion is not very distinct, whereas its position in the middle of the median border to one side of the distal end of the facet for the supinator brevis is clearly marked both in the Lion and in the Leopard. The relative proportions of the distal end and of the styloid process are well shown in the figure. So far as the grooves for the extensor tendons are concerned, the Lion differs from the Leopard, and makes some approach to the Cheetah, in that those grooves in which lie the extensor carpi radialis and extensor carpi obliquus are somewhat narrower and deeper. In the Cheetab this process has been carried further and extended to the groove for the extensor communis digitorum. In none of the three is the groove for the extensor lateralis digitorum very distinct ; it is best displayed in old male Lions. The facet which articulates with the distal end of the ulm is relatively large and distinct in the Lion and Leopard, but small and not well defined in the Cheetah. The distal articular surface is 'concave in all Wections, except where it pws~eson to the styloid process. There it tends to become convex in the volar dorsal direction, with the greatest convexity at t 'e volar margin. This distal facet is broader and shallower in the Lion and Leopar , narrower and deeper in the Cheetah. The foregoing account of t h e radius shows that the muscles of pronation and supination are more highly developed in the Leopard than they are in the Cheetah, and that the Lion is intermediate between the other two. Contrariwise, t h e extensor muscles of the Cheetah are relatively stronger than those of the Leopard, and again the Lion is intermediate. Once more the findings are what one might have anticipated from a general knowledge of the habits of the animals, for it is obvious that the power of rotating the forearm is of greater importance to a climbing species than it is to a cursorial one, and that powerful extensors are more likely to be foundin the latter, where they are so valuable in maintaining the straightness and rigidity of the manus needed if the maximum speed is 50 be developed. The flexor muscles, on the other hand, are of greater importance to climbing animals, and we do in fact find that the origin of the deep digital flexor is clearly defined on the radius of the Leopard, and SO 2 266 DR. A. "DELL HO$?WOOD ON on that of the Lion, but that there is no particular feature to indicate its presence in the Cheetah. Ulna. The proximal surface of the olecranon presents a domed fairly smooth, posterior area, and in front of it a deep fossa with prominent margins, one of them stronger and in advance of the other. The long head of the triceps is inserted to the posterior area ; the medial head to the medial margin of the fossa. and the anconaeus to the lateral margin. There are significant differences in the developmentjof the margins of the fossa. l n the Leopard the lateral margin ici thick and tumid ; it ix pushed forwards in front of the medial margin, which in thin and sharp. In the Lion, too, the lateral marghi of the fossa is the xtrongcr and more forwardly situated of the two, but the medial FIG. :<.-Diagram of the liretl of the ulna seen from in front, to show the position of the ridge in the sigmoid notrh i n the Leopard (dotted), Lion (continuous), and Chertah (heavy). (The right side ofthe figure is the lateral side of the bone). margin is relatively higher and stronger than it is in the Leopard. In the Cheetah the conditions are reversed and the medial margin is bigger, stronger, and more forwardly situated than the lateral. From these observations one may deduce that the Leopard has the anconaeus stronger than the medial head of the triceps ; that in the Lion the mconaeus is still the stronger, although the difference between the two muscles is less marked ; and that in the Cheetah the medial head of the triceps is much stronger than the head of the anconaeus. CONTRIBUTIONS TO THE STUDY Ol? SOME A*RICAN MAMBfALS 267 The explanation of these variations in structure is evident when the greater sigmoid notch of the ulna is examined. This looks forwards and upwards, is concave from above downwards, and is divided by a low rounded ridge which extends from the anconeal process above to the lateral margin of the coronoid process below. If the plane of the ridge be continued upwards it cuts the proximal surface of the ulna in various ways, thus. In the Leopard it passes through the lateral lip, to which the anconaeus is inserted; in the Lion it passes through the floor of the fossa, slightly nearer to the lateral than to the medial lip ; in the Cheetah it paases through the medial lip, t o which the medial head of the triceps is inserted : this indicates a gradual migration of the longitudinal axis of the elbow-joint from without (Leopard) inwards (Cheetah), and a lessening of the angle between that axis and the long axis of the bone with the result that the forearm of the Cheetah moves more nearly in the same plane as the upper arm, whereas in the Leopard there is a marked difference between the two planes. Both muscles are extensors of the elbow, and supplement the action of the long head of the triceps ; in addition they act as guides or distributors of the extending force and ensure that a proper proportion is applied to keeping the ridge of the sigmoid notch running truly within the groove of the trochlea of the humerus. The shaft and distal end of the ulna are stout and well developed in the Lion and Leopard ; although the latter is perhaps the more slender,there are no great differences between them. Each has a prominent somewhat domed facet by which it articulates with the lower end of the radius and, separated from it by a deep notch, another facet of like character on the styloid process for articulation with the cuneiform and pisiform. In the Cheetah the shaft of the ulna is much more slender than in either of the other two species, and the distal end by no means so well developed. The facet for articulation with the distal end of the radius is greatly diminished and that for articulation with the cuneiform and pisiform, though distinct, is smaller still. The reduction of the shaft of the ulna and of its distal end in the Cheetah are bound up with a loss of the power of rotating the bones of the forearm, a function which ceases to be of use as the specialization for speed increases, Carpus and Metacarpw. The carpus and metacarpus are most profitably to be considered as interarticulating units, and it is the nature of the articulations as entities rather than detailed descriptions of the individual bones which is significant. There are three joints involved, namely, the wrist, or radio-carpal, joint ; the intercarpal joint ; and the carpo-metacarpal joint. Of these the shape ofthe first governs the movement of the wrist and hand relative to the forearm, the second gives added flexibility t o the carpus and plays a major part in determining the degree of lateral motion of which the metacarpals are capable, and the third is largely concerned with the flexion and extension of the hand. The radio-carpal joint is that between the distal end of the radius and the scapholunar bone. The radial facet of the latter is convex in both the medio-lateral and dorsi-volar directions and the former line is continued, laterally by the proximal ulnar, facet of the cuneiform. The dorsi-volar convexity is greatest on the lunar portion of the scapho-lunar and less on the scaphoid portion where it passes behind into a transverse concavity with a stout upward projection or lip. The lunar concavity in the Leopard is roughly hemispherical whereas the scaphoidal portion is somewhat flattened. In the Lion the lunar portion tends to be produced transversely to form a ridge. This is carried further in the Cheetah, so that a definite ridge extends right t o the medial margin. The posterior lip of the concavity acts as a check ; it works into a small facet volar-lateral to, and just at the root of the styloid process of the radius, and limits flexion of the joint. The transverse contour of the scapho-lunar is very nearly an arc of a circle, and the corresponding contour of the ulnar facet of the cuneiform is also an arc of a circle which is of greater radius than, and excentric to, the former. Consequently, lateral 268 bR. A. ~TNDELLHOPWOOD ON motion of the wrist and hand on the forearm must entail a certain degree of separation between the distal ends of the radius and ulna, the separation being greatest in the Leopard, less in the Lion and least in the Cheetah. I n none of the three species is there tnie articulation between the scapho-lunar and the cuneiform ; the connexion is ligamentous. Extensive facets prove that the cuneiform and pisiform are in direct contact. The ulnar facet is largest and flattest in the Leopard, smallest in the Cheetah, and intermediate in extent but most deeply concave in the Lion. The distal row of the carpus divides naturally into a radial portion (trapezium, trapezoid, magnum) and an ulnar portion (unciform), but the manner of its working is not YO simple. The inciform has a lunar facet which is convex in front, and concave behind ; the motion of the bone is dorsi-volar. The radial portion of the second row of the carpus divides into two parts, namely, the magfium, and the trapezoid -Cu .-Pi. sc.- Lu.- Cu.- Pi. FIG.4.--Carpal diagrams of a mesonyrhid creodont ( A ) and a hippopotamus (13). Full I1rms indicate primary, and broken lines secondary. contacts. Compare with fig. 5 on thc facing page, with the trapezium. The general direction of movement of the latter is conditioned by an oblique ridge which crosses the distal surface of the scapho-lunar from the antero-external t o the postero-internal angle, and which engages with tt groove on the proximal surface of the trapezoid. In the Lion and Leopard, but not in the Cheetah, this groove continues on t o part of the proximal surface of the trapezium. Movement of the magnum is governed by an oblique groove which is t o the ulnar side of the ridge just mentioned, and more directly dorsi-volar in direction ; it engages with the proximal ridge of the magnum. I n brief, there are three directions of movement of the distal row of carpal bones, all of them spreading fan-wise from the dorso-lateral angle of the scapho-lunar. I n the Lion and the Leopard the ridge for the trapezoid and the groove for the magnum cut the dorsal border of the inferior facet of the scapho-lunar a t angles of about 38" and 67"respectively. I n the Cheettahthe groove for the magnum is strongly marked, but the ridge for the trapezoid is so greatly reduced that its value as a guide CONTRIBUTIONS TO THE STUDY OP SOME APRICAN MAMMALS ' 269 is doubtful. Since the direction of the groove for the magnum has become more nearly dorsi-volar a t the same time, and is now sub-parallel t o the facet for the unciform, the effect is that the metacarpus and digits of the Cheetah are not so capable of being spread apart, and are forced t o work more in one plane than they do in either of the other two species. The carpo-metacarpal joint divides naturally into radial and ulnar portions. The radial portion consists of the first three carpals and metacarpals, and the ulnar portion of the unciforni with the fourth and fifth metacarpals. Taken as a whole, the individual carpal bones are wedge-shaped, the dorsal surface being wider than thc volar, so they form an arch of which the convexity is on the dorsal surface. Tho bases of the second and third metacarpals are also wedge-shaped (the much reduced first metacarpal may be ignored) and the grooves and ridges on their proximal surfact,s tlivtrgc radially from a point behind the volar concavity to work against similarly divergent ridges and grooves on the distal facets of the second and third carpals. LU.- sc. .. I II I sc. iii Lu. 1- rv v Cu.-Pi. FIG. S.--Ctlrpal diagrams of a rniacid credolit (A) and the three cats desc.ribud in this paper (B). The contact between the magnum and the fourth metacarpal is indicated by the dotted line. Compare with fig. 4 on the facing page. The bases of the fourth and fifth metacarpals are pressed closely together so their proximal articular surfaces form what is in effect a single segment of a transverse cylinder which articulates with the inferior facet of the unciform. A small facet on the postero-radial corner of the base of the fourth metmacarpalarticulates with the postero-ulnar corner of the magnum : it tends to be relatively larger in the Leopard than it is either in the Cheetah or in the Lion. The distinctions between the carpo-metacarpal joints of Lion, Leopard, and Cheetah are, broadly speaking, of the same order as those already noted in other parts of the limb. I n the Lion and Leopard the grooves and ridges on the radial portion are divergent and well-marked, whereas in the Cheetah they are sub-parallel, less distinct, and the whole surface of the distal carpals on which they occur is very much flatter in the Cheetah than in the other two species. The inter-metacarpal 210 DR. A. TINDELL HOPWOOD 0~ articulations are best developed and most clearly defined in the Lion, and only less SO in the Leopard. In the Cheetah they are reduced and by no means so clearly defined. The differences noted between the articulations of wrist and hand of the Leopard and those of the Cheetah have the effect of restricting the range of movement of the latter. The radial-carpal articulation of the Leopard approximates to a universal joint, but the transverse extension of the convexity of the proximal facet of the scapho-lunar bone in the Cheetah limits the range of motion so severely that the universal joint of the Leopard, and to a lesser extent that of the Lion, is changed into a hinge which for all practical purposes moves only in an anterior-posterior direction. Similarly, the intercarpal joints of the Cheetah prevent that spreading of the metacarpus and digits which is so well developed in the Leopard and Lion. This restriction cf movement is further reflected in the metacarpals of the Cheetah, the heads of which have the proximal facets much flattened. Moreover, the Cheetah has the metacarpals pressed closely together so that the third and fourth metacarpals incline to function as a unit, and the whole hand takes on a markedly artiodactyl character. Discussion.-Owing t o the form of the bones and the disposition of the muscles, the fore-limb of the Leopard is capable of a greater range and variety of movement than is that of the Cheetah ; the Lion comes somewhere in between the other two. The modifications of the Cheetah away from the general feline pattern are all in the direction of speed. They result in a diminution of the abductor function, in a pronounced tendency to restrict the limb to a backwards and forwards movement, in loss of the power of rotating the bones of the fore-limb, in a great reduction of the mobility of the carpus, and in pronounced artiodactyly of the metacarpus and digits. The artiodactyly of the carnivore foot was first described by Boas, but his observations were confined to external characters. He also showed that artiodactyly, which is general and often well-marked among the Cainivora, occurs sporadically in other orders. There is, however, this difference, that whereas all genera of carnivores have paraxonic hands and feet, the other orders may also contain genera in which the symmetry is of the perissodactyl type (mesaxonic),and even genera in which the hand is of one type of symmetry and the foot of the other. Boas gives two examples among the rodents : Hydrochoerus has niesaxonic hands and feet, whereas the hares have a mesaxonic hand and a paraxonic foot. Primitive artiodactyls preserve the original relationships of the distal carpalia to the metacarpalia almost unchanged. In them Mc I articulates with the trapezium, Mc I1 with the trapezoid, Mc I11 with the magnum, and Mc IV and V with the unciform. In some, at least, of the modern carnivora there is a small contact between the head of Mc IV and the volar-radial corner of the distal surface of the magnum, but this appears to be a feature which has developed pari p s u with the gradual increase in size of the magnum. It is present on a few bones found in the Upper Eocene of France, and on bones found in later deposits, but it does not seem to be at all a constant feature until modern genera appear, and even in them there is reason to suppose that it is more regular in its development in the later species than it is in the earlier ones. Apart from this one character of doubtful value and meaning, the relations between the carpals and metacarpals are similar to those which obtain in that section of artiodactyls termed by Kowalevsky Artiodactyla Inadaptiva. The differences which develop between the two orders when the carpal elements begin to fuse are also important. In the Carnivora the first step is for the centrale to unite with the scaphoid, and the next for the scapho-centraleto unite with the lunar to form the familiar scapho-lunar of the true carnivores. The Eocene Miacidae either have all the bones separate, or at the most a scapho-centrale, but one species, VuZpavus projectus, has a scapho-lunar of the modern type. The elements of the distal row never fuse in carnivores. CONTRIBUTIONS TO THE STUDY OF SOME AFRICAN MAMMALS 271 The artiodactyls, on the other hand, retain the discrete proximal row of carpal bones ; gradually lose the centrale, which never appears in recent genera, even as a cartilaginous vestige in the embryo ; and restrict fusion of the carpal elements to the radial side of the distal row. Afj a general rule, fusion takes place in the didactyl genera only, and the tetradactyl genera remain in the primitive condition, but there are exceptions. For example, the camel has all the bones of the carpus separate, and Caerwtherium, an extinct tetradactyl genus, contains some species in which the trapezium, trapezoid, and magnum, are fused to form a single bone. These observations indicate that although the Carnivora resemble the Artiodactyla in the symmetry of the metacarpus, they differ fundamentally in the characters of the carpus, and it might be thought that the resemblances were due to convergence. The true explanation is that the conditions governing the future evolution of the carnivore foot were laid down at the very beginning of the Tertiary, when the Miacidae, for ressons not yet fully understood, acquired a paraxonic symmetry. Once that had happened it was inevitable that further adaption towards a cursorial life should follow the wme general lines as that of the artiodactyls, which also derive from a very primitive stock with paraxonic feet, the Mesonychidae, At the same time, it was not possible for the carnivores to follow exactly the same path as that trodden by the artiodactyls because the characters of the carpus differ, but it is worth remembering that the tendency so to do WM very marked, and that the carnivores underwent a reduction of digits in the same manner, though not to the same degree, as the Artiodactyla Inadaptiva.