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SKELETON OF THE ANT-EATER.

osseous carapace, as the tie-bearers" have to the "king-post" in the architecture of a roof.

Skeleton of the Mole.-The mole is hardly less fitted for the actions of an ordinary land-quadruped than the sloth; but the one is as admirably constructed for subterraneous as the other for arboreal life. The fore-limbs are as remarkably short, broad, and massive in the mole, as they are long and slender in the sloth; yet the same osseous elements, similarly disposed, occur in the skeleton of each. The head of the mole is long and cone-shaped; its broad base joins on the trunk without any outward appearance of a neck. The fore-part

of the trunk, to which the principal muscular masses working the fore-limbs are

Fig. 41.

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SKELETON OF THE MOLE.

attached, is the thickest, and thence the body tapers to the hind-quarters, which are supported by limbs as slender as they are short.

The neck-bones, nevertheless, are not wanting; they even exist in the same number as in the giraffe; the vertebral formula of the mole being-7 cervical, 13 dorsal, 6 lumbar, 5 sacral, and 10 caudal. The spine of the second vertebra or dentata is large, and extended back over the third vertebra: the neural arches of this and the succeeding neck-vertebræ form thin simple arches without spines: the entire vertebræ have been described as mere rings of bone; but the transverse processes of the fourth, fifth, and sixth cervicals are produced forwards and backwards, and overlap each other: in the seventh vertebra those processes are reduced to tubercular diapophyses which are not perforated: the bodies of the vertebræ are depressed and quadrate. The part answering to the nuchal ligament in the giraffe is bony in the mole, u.

The first sternal bone, or manubrium, is of unusual length, being much produced forwards, and its under surface downwards in the shape of a deep keel for extending the origin of the pectoral muscles. Seven pairs of ribs directly join the sternum, which consists of four bones, in addition to the manubrium and an ossified ensiform appendage. The neural spines, which are almost obsolete in the first eight dorsals, rapidly gain length in the rest, and are antroverted in the last two dorsal vertebræ. The diapophyses, being developed in the posterior dorsals, determine the nature of the longer homologous processes in the lumbar vertebræ.

The lumbar spines are low, but of considerable antero-posterior extent: the diapophyses are bent forward in the last four vertebræ a small, detached, wedgeshaped hypapophysis is fixed into the lower interspace of the bodies of the lumbar vertebræ.

The scapula, 51, is very long and narrow, but thick, and almost three-sided: the common rib-shape is resumed in this cranial pleurapophysis, as we have seen in the bird and tortoise. The clavicle, on the other hand, instead of the usual long and slender figure, presents the form of a cube, being very short and broad, articulated firmly to the anteriorly projecting breast-bone, and more loosely with the acromion and head of the humerus.

This bone, 53, would be classified amongst the "flat" bones. It is almost as broad as it is long, especially at its proximal end, which presents two articular surfaces-one for the scapula, the other for the clavicle: the expanse of the bone beyond these surfaces relates to the formation of an adequate extent of attachment for the deltoid, pectoral, and other great burrowing muscles. All the other bones of the fore-limb are as extremely modified for fossorial actions. The olecranon expands transversely at its extremity, and the back part of the ulna is produced into a strong ridge of bone.

The shaft of the radius is divided by a wide interosseous space from the ulna, and the head of the radius is produced into a hook-shaped process like a second "olecranon." The carpal series consists of five bones in each row-the scaphoid being divided in the first, and a sesamoid being added to the second row; moreover, there is a large supplementary sickle-shaped bone, extending from the radius to the metacarpal of the pollex, giving increased breadth and a convex margin to the radial side of the very powerful hand, and chiefly completing its adaptation to the act of rapidly displacing the soil. The phalanges of the fingers are short and very strong: the last are bifid at their ends for a firmer attachment of the strong claws. Little more of the hand than these claws, and the digging or scraping edge, projects beyond the sheath of skin enveloping the other joints, and connecting the hand with the trunk.

The common position of the arm-bone is with its distal end most raised. The forearm, with the elbow raised, is in the state between pronation and supination, the radial side of the hand being downwards, and the palm directed outwards. The whole limb, in its position and structure, is unequalled in the vertebrate series as a fossorial instrument, and only paralleled by the corresponding limb in the mole-cricket (Gryllotalpa) amongst the insect-tribes.

No impediment is offered by the hinder parts of the body or limbs when the thickest part of the animated wedge has worked its way through the soil. The pelvis is remarkably narrow. The ossa innominata have coalesced with the sacrum but not with each other, the pubic arch remaining open. The bodies of the sacral vertebræ are blended together, and are carinate below; their neural spines have coalesced to form a high ridge. The acetabula look almost directly outwards. The head of the femur has no pit for a round ligament. A fabella is preserved behind the outer condyle. A hamular process is sent off from the head of the tibia and fibula; the lower moieties of the shafts of these bones are blended together. The toes are five in number on the hind-feet as in the fore, but are much more feebly developed. They serve to throw back the loose earth detached by the spade-shaped hands.

Skeleton of the Bat.-The form of limb presented by the arm and hand of the bat offers the most striking contrast to the burrowing trowel of the mole. Viewed in the living animal it is a thin, widely-expanded sheet of membrane, sustained like an umbrella by slender rays, and flapped by means of these up and down in the air, and with such force and rapidity, as, combined with its extensive surface, to react upon the rare element more powerfully than gravitation can attract the weight to which the fore-limbs are attached; consequently the body is raised aloft, and

borne swiftly through the air. The mammal now rivals the bird in its faculty of

Fig. 42.

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progressive motion; it flies, and the instruments of its aërial course are called "wings." The whole frame of the bat is in harmony with this faculty, but the mamalian type of skeleton is in nowise departed from.

The vertebral formula of the common bat (Vespertilio murinus) (Fig. 42), is7 cervical, 12 dorsal, 7 lumbar, 3 sacral, and 8 caudal vertebræ. The chief characteris tics of the skeleton are-the gradual diminution of size of the spinal column from the cervical to the sacral regions; the absence of neural spines in the vertebræ beyond the dentata; a keeled sternum; long and strong, bent clavicles, 58; broad scapulæ, 51; elongated humeri, 53; more elongated and slender radius, 55; and still longer and more slender metacarpals and phalanges of the four fingers, ii, iii, iv, v, which are without claws, the thumb, i, being short and provided with a claw: the pelvis, 62, is small, slender, and open at the pubis, 63; the fibula, 67, is rudimental, like the ulna, 54, in the fore-arm. The common bat has a long and slender stiliform appendage to the heel, 68, which helps to sustain the caudo-femoral membrane. The hind digits are five in number, short, subequal, each provided with a claw; they are the instruments by which the bat suspends itself, head downwards, during its daily summer sleep, and continued winter torpor.

SKELETON OF THE BAT (Vespertilio murinus).

Skeleton of the Carnivorous Mammalia.-The lion may be regarded as the type of a quadruped. The well-adjusted proportions of the head, the trunk, the fore-limbs, and tail concur with their structure to form an animal swift in course, agile in leaps and bounds, terrible in the overpowering force of the blows inflicted by the fore-limbs. The strong, sharp, much-curved, retractile talons terminating the broad powerful feet, enable the carnivore to seize the prey it has overtaken, and to rend the body it has struck down. The jaws have a proportional strength, and are armed with fangs fitted to pierce, lacerate, and kill.

The carnivorous character of the skull, as exemplified by the sagittal and occipita crests, by the strength and expanse of the zygomatic arches, by the breadth, depth, and shortness of the jaws, by the height of the coronoid processes, and by the depth and extent of the fosse of the lower jaw for the attachment of the biting muscles, reaches its maximum in the lion. The triangular occipital region is remarkable for the depth and boldness of the sculpturing of its outer surface, indicative of the powerful muscles working the whole skull upon the neck and trunk. The conjoined paroccipitals and mastoids form a broad and thick capsular support for the back part of the acoustic bullæ. The pterygoid processes are imperforate. A well-marked groove extends on each side of the bony palate from the posterior to the anterior palatine foramina. The

premaxillaries are comparatively short, and one-half of the lateral border of the nasals directly articulates with the maxillaries. The antorbital foramina are largely indicative of the size of the sensitive nerve supplying the well-developed whiskers. Within the cranium we find that ossification has extended into the membrane dividing the cerebrum from the cerebellum. This bony tentorium extends above the petrosal to the ridge overhanging the Gasserian fossa; the petrosal is short, its apex is neither notched nor perforated; the cerebellar pit is very shallow. The sella turcica is deep, and well defined by both the anterior and posterior clinoids. The rhinencephalic fossa is relatively larger in the lion than in most carnivora, and is defined by a well-marked angle of the inner table of the skull from the prosencephalic compartment. The olfactory chamber extends backwards both above and below the rhinencephalic fossa; the upper part of the chamber is divided into two sinuses on each side. The superior turbinals extend into the anterior sinus, and below into the presphenoidal sinus. All the bones of the skeleton are remarkable for their whiteness and compact structure.

The vertebral formula of the lion (Fig. 43) is-7 cervical, 13 dorsal, 7 lumbar, 3 sacral, and 23 caudal. The last cervical vertebra has the transverse processes imperforate, being formed only by diapophyses. The eleventh dorsal is that toward which the spines of the other trunk-vertebræ converge, and indicates the centre of motion of the trunk in this bounding quadruped. Eight pairs of ribs directly join the sternum, which consists of eight bones. The clavicles are reduced to clavicular bones, 58, suspended in the flesh. The supraspinal fossa of the scapula is less deep than the infraspinal one, and its border is almost uniformly convex; the acromion is bifid, the recurved point being little larger than the extremity or anterior point. The humerus, 53, is perforated above the inner condyle, but not between the condyles. The radius, 55, and ulna, 54, are so articulated as to permit a free rotation of the forepaw. The scaphoid and lunar bones are connate. Besides these, the bones of the

carpus are the cuneiforme; the pisiforme; the trapezium, which gives an articulation to the ulnar side of the base of the short metacarpus of the pollex; the trapezoides; the magnum, which is the least of the carpal bones; the unciforme, which supports, as usual, the metacarpals of the fourth and fifth digits; and the pisiforme, which projects far backwards, like a small calcaneum: there is also a supplementary oscicle wedged in the interspace between the prominent end of the scapho-lunar bone and the proximal end of the metacarpal of the pollex. The pollex is retained on the fore-foot, and, like the other toes, is terminated by a large, compressed, retractile, ungual phalanx, forming a deep sheath, for the firm attachment of the large curved and sharp-pointed claws.

The pelvis, 62, 63, 64, the femur, 65, the tibia, 66, and fibula, 67, offer no remarkable modifications of structure; the patella, 66, is well ossified, and there is a fabella, 67, behind each condyle of the femur. The tarsal bones are the astragalus; the scaphoides; the calcaneum; the cuboides, which, like the unciforme in the carpus, supports the two outer digits; the cuneiforme externum, which, like the magnum, supports the middle digit; the cuneiforme medium, which, like the trapezoides, supports the second digit; and the cuneiforme internum, which supports the rudiment of the metatarsal of the first or innermost digit.

The last or ungual phalanx, in both fore and hind feet, has a bony sheath at its base for the firmer implantation of the claw; and its joint is at the back part of the proximal end of the phalanx, whereby it can be drawn upwards upon the second phalanx, when the claw becomes concealed in the fold of integument forming the interspace of the digits.

This state of retraction is constantly maintained, except when overcome by an extending force, by means of elastic ligaments. The principal one arises from the outer side and distal extremity of the second phalanx, and is inserted into the superior angle of the last phalanx; a second arises from the outer side and proximal end of the second phalanx, and passes obliquely to be inserted at the inner side of the base of the last phalanx. A third, which arises from the inner side and proximal extremity of the second phalanx, is inserted at the same point as the preceding. The tendon of the flexor profundus perforans is the antagonist of the elastic ligaments. By the action of that muscle the last phalanx is drawn forwards and downwards, and the claw exposed. In order to produce the full effect of drawing out the claw, a corresponding action of the extensor muscle is necessary, to support and fix the second phalanx; by its ultimate insertion in the terminal phalanx, it serves also to restrain and regulate the actions of the flexor muscle. As the phalanges of the hind-foot are retracted in a different direction to those of the fore-foot, i. e. directly upon, and not by the side of the second phalanx, the elastic ligaments are differently disposed, but perform the same main office. It seems scarcely necessary to allude to the final intention of these beautiful structures, which are, with some slight modifications, common to the genus Felis. The claws being thus retracted within folds of the integument, are preserved constantly sharp, and ready for their destined functions, not being blunted and worn away in the ordinary progressive motions of the animal; while at the same time the sole of the foot, being padded, such soft parts only are brought in contact with the ground as conduce to the noiseless tread of the stealthy feline tribe. This highly-developed unguiculate structure with the dental system and concomitant modifications of the skull, completes the predatory character of the typical Carnivora.

Skeleton of the Kangaroo.-Australia possesses an indigenous race of herbivorous mammals created to enjoy existence on its grassy plains. But the climate of this fifth