Download Contributions to the study of some African Mammals.III. Adaptations

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
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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
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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
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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
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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.