Page:EB1911 - Volume 05.djvu/380

 there is never an os centrale in the adult; and the fibula is distinct.

The large majority of the species subsist chiefly on animal food, though many are omnivorous, and a few chiefly vegetable-eaters. The more typical forms live altogether on recently-killed warm-blooded animals, and their whole organization is thoroughly adapted to a predaceous mode of life. In conformity with this manner of obtaining their subsistence, they are generally bold and savage in disposition, though some are capable of being domesticated, and when placed under favourable circumstances exhibit a high degree of intelligence.

The typical section of the group, the Carnivora Vera, Fissipedia or Carnassidentia, includes all the existing terrestrial members of the order, together with the otters and sea-otters. In this section the fore-limbs never have the first digit, or the hind-limbs the first and fifth digits, longer than the others; and the incisors are $3⁄3$ on each side, with very rare exceptions. The cerebral hemispheres are more or less elongated; always with three or four convolutions on the outer surface forming arches above each other, the lowest surrounding the Sylvian fissure. In the cheek-series there is one specially modified tooth in each jaw, to which the name of “sectorial” or “carnassial” is applied. The teeth in front of this are more or less sharp-pointed and compressed; the teeth behind broad and tuberculated. The characters of the sectorial teeth deserve special attention, as, though fundamentally the same throughout the group, they are greatly modified in different genera. The upper sectorial is the most posterior of the teeth which have predecessors, and is therefore reckoned as the last premolar ( p. 4 of the typical dentition). It consists of a more or less compressed blade supported on two roots and an inner lobe supported by a distinct root (see fig. 1). The blade when fully developed has three cusps (1, 2 and 3), but the anterior is always small, and often absent. The middle cusp is conical, high and pointed; and the posterior cusp has a compressed, straight, knife-like edge. The inner cusp. (4) varies in extent, but is generally placed near the anterior end of the blade, though sometimes median in position. In the Ursidae alone both the inner cusp and its root are wanting, and there is often a small internal and posterior cusp (5) without root. In this family also the sectorial is relatively to the other teeth much smaller than in other Carnivora. The lower sectorial (fig. 2) is the most anterior of the teeth without predecessors in the milk-series, and is therefore reckoned the first molar. It has two roots supporting a crown, consisting when fully developed of a compressed bilobed blade (1 and 2), a heel (4), and an inner tubercle (3). The cusps of the blade, of which the hinder (2) is the larger, are separated by a notch, generally prolonged into a linear fissure. In the specialized Felidae (I) the blade alone is developed, both heel and inner tubercle being absent or rudimentary. In Meles (V) and Ursus (VI) the heel is greatly developed, broad and tuberculated. The blade in these cases is generally placed obliquely, its flat or convex (outer) side looking forwards, so that the two lobes or cusps are almost side by side, instead of anterior and posterior. The inner tubercle (3) is generally a conical pointed cusp, placed to the inner side of the hinder lobe of the blade. The special characters of these teeth are more disguised in the sea-otter than in any other species, but even here they can be traced.

The toes are nearly always armed with large, strong, curved and sharp claws, ensheathing the terminal phalanges and held firmly in place by broad plates of bone reflected over their attached ends from the bases of the phalanges. In the Felidae these claws are “retractile”; the terminal phalange with the claw attached, folding back in the fore-foot into a sheath by the outer or ulnar side of the middle phalange of the digit, and retained in this position when at rest by a strong elastic ligament. In the hind-foot the terminal joint or phalange is retracted on to the top, and not the side of the middle phalange. By the action of the deep flexor muscles the terminal phalanges are straightened, the claws protruded from their sheath, and the soft “velvety” paw becomes suddenly converted into a formidable weapon of offence. The habitual retraction of the claws preserves their points from wear.

The land Carnivora are best divided into two subgroups or sections—(A) the Aeluroidea, or Herpestoidea, and (B) the Arctoidea; the recognition of a third section, Cynoidea, being rendered untenable by the evidence of extinct forms.

(A) Aeluroidea.—In this section, which comprises the cats (Felidae), civets (Viverridae), and hyenas (Hyaenidae), the tympanic bone is more or less ring-like, and forms only a part of the outer wall of the tympanic cavity; an inflated alisphenoid bulla is developed; and the external auditory meatus is short. In the nasal chamber the maxillo-turbinal is small and doubly folded, and does not cut off the naso-turbinal and adjacent bones from the nasal aperture. The carotid canal in the skull is short or absent. Cowper’s glands are present, as is a prostate gland and a caecum, as well as a duodenal-jejunal flexure in the intestine, but an os penis is either wanting or small.

The members of the cat tribe, or Felidae, are collectively characterized by the following features. An alisphenoid is lacking on the lower aspect of the skull. In existing forms the usual dental formula is i. , c. , p. , m. ; the upper molar being rudimentary and placed on the inner side of the carnassial, but the first premolar may be absent, while, as an abnormality, there may be a small second lower molar, which is constantly present in