The skull of nearly all Carnivora is distinguished from that of most other Mammals by its immense strength, and its evident adaptation to the habits of its possessor—to the effective seizing and devouring of living prey. It is remarkable for the immense roughened bony ridges, developed in many parts of it, which serve for the attachment of the mighty jaw-muscles, the great size of which causes an increase in the width of the bony jugal arch, extending from under the eye to just in front of the ear. Another point worthy of notice is the great shortening of the jaws, or of the facial in relation to the cranial portions of the skull. In this respect Carnivores, especially the most typical forms, the Cats, are very markedly distinguished from Herbivores, in which the brain-case is small and the face immensely prolonged. This has to do with the different kind of food used by the two groups—that of vegetable-eaters requiring long grinding, that of flesh-eaters powerful mincing. Connected also with this same function of mastication is the form of the condyle, or bony projection of the lower jaw, by which it moves on the skull, and of the smooth surface of the latter which receives it. These are in Carnivora greatly elongated transversely, and narrowed from before backwards, so that no motion from side to side, but only an up-and-down motion, is possible. The higher Carnivora, therefore, cannot chew or grind their food, but only mince it, their sharp teeth acting exactly like scissor-blades. In the interior of the skull should be noticed a large plate of bone which extends inwards and separates the great brain, or cerebrum, from the lesser brain, or cerebellum, and prevents the jarring of that important organ likely to arise from the animal’s vigorous movements.
SKELETON OF LION.
In the spine, or vertebral column, there is not much to notice beyond the great size of the first two vertebræ, or those which support the head, and the development of strong spines or processes for the attachment of muscles.
SKELETON OF POLAR BEAR.
In the limbs there are certain points of considerable interest and importance. If a Bear and a Lion be watched while walking, a great difference will be observed in their gait: the Bear’s movements are far clumsier and less springy than those of the Lion. A little further observation will show that this is due, chiefly, to the manner in which their feet are set on the limbs, for it will be seen that the Bear keeps the sole of his foot flat on the ground, and, as his foot is very large, he has something of the awkward, sprawling movement of a man walking in shoes too big for him. The Lion, on the other hand, has his wrist and his heel lifted well above the ground, and so walks, not on the sole of his foot, but on his toes, the under surfaces of which are furnished with beautifully soft leathery pads, so as to ensure a soft, silent footstep. Then what looks like the knee of a Lion, Cat, or Dog is really his wrist. and what looks like a backward turned knee in his hind leg is his heel, the true elbow and knee being almost hidden by the skin.
The reason of this arrangement is seen by looking at the skeletons of the two animals. In the Bear the metacarpals and metatarsals, or five long bones extending between the wrist and the ankle respectively, and the joints of the toes, are kept in a horizontal position, as in ourselves; in the Lion, on the contrary, the metacarpals and metatarsals are lifted almost into a vertical position, the walking surface being now afforded by the under surface of the toe-bones, or phalanges. By reason of this the Lion gets an extra lever in his leg, in addition to the two levers which the Bear possesses, namely, those afforded by the bones of the arm and fore-arm and of the thigh and leg respectively; and consequently his springiness is greatly increased. An animal which walks like the Bear, on the sole of its foot, is said to be plantigrade: one which walks on its fingers, like the Lion, Cat, or Dog, is called digitigrade.
As in all animals in which the fore limbs are used for support, and not for prehension, the collar-bone, or clavicle, is either wholly absent or quite rudimentary, and the fore limb has therefore no bony connection with the trunk, but is attached simply by muscles and ligaments. The Carnivores, in leaping or running, often come down with their whole weight upon the fore legs, and if a large bony clavicle, like that of a Monkey or Bat, were present, it would infallibly be broken.