Page:Encyclopædia Britannica, Ninth Edition, v. 15.djvu/457

Rh CAKNIVORA.] M A M MALI A 433 they must be distinguished. They are unguiculate, and have never less than four well-developed toes on each foot, with nails more or less pointed, rarely rudimentary or absent. The pollex and hallux are never opposable to the other digits. They are regularly diphyodont and hetero- dont, and their teeth are always rooted. 1 Their dentition consists of small pointed incisors, usually three in number, on each side of each jaw, of which the first is always the smallest and the third the largest, the difference being most marked in the upper jaw ; strong conical, pointed, recurved canines ; molars variable, but generally, especially in the anterior part of the series, more or less compressed, pointed, and trenchant ; if the crowns are flat and tuberculated they are never complex or divided into lobes by deep inflexions of enamel. The condyle of the lower jaw is a transversely placed half-cylinder working in a deep glenoid fossa of corresponding form. The brain varies much in relative size and form, but the hemispheres are never destitute of well-marked convolutions. Tha stomach is always simple and pyriform. The cascuin is either absent or short and simple, and the colon is not sacculated or greatly wider than the small intestine. Yesicube seminales are never present. Cowpsr s glands are present in some, absent in other groups. The uterus is bicornuate. The mammas are abdominal, and very variable in number. The placenta is deciduate, and almost always zonary. The clavicle is often entirely absent, and when present is never complete. The radius and ulna are distinct. The scaphoid and lunar bones are always united into one, and there is never a distinct os ceutrale in the adult. The fibula is always a distinct slender bone. The large majority of the species composing this order subsist chiefly upon some variety of animal food, though many are omnivorous, and some few chiefly, though not entirely, vegetable eaters. The more typical forms live altogether on recently-killed warm-blooded animals, and their whole organization is thoroughly adapted to a pre- daceous mode of life. In conformity with this manner of obtaining their subsistence they are generally bold and savage in disposition, though some species are capable of being domesticated, and when placed under favourable circumstances for the development of such qualities exhibit a very high degree of intelligence and fidelity. The order is naturally divided into two suborders, the members of one being the more typical, and mainly terrestrial in their mode of life, while those of the other are aberrant, having the whole of their organization specially modified for living habitually in water. These are called respectively the True or Fissiped and the Pinniped Carnivora. SUBORDER CAUNIVORA VERA OR FISSIFEDIA. Generally adapted for terrestrial progression and mode of life, though some may be partially aquatic in their habits. The fore limbs never have the first digit, or the hind limbs the first and fifth digits, longer than the others. Incisors J on each side, with very rare exceptions. Cerebral hemispheres more or lesa elongated ; always with three or four gyri on the outer surface forming arches above each other, the lowest surrounding the Sylvian fissure. The molar series of teeth have not the uniform characters of those of the Pinnipedla. There is always one tooth in each jaw which is specially modified, and to which the name of &quot; sectorial &quot; or &quot; carnassial &quot; tooth has been applied. The teeth in front of this are more or less sharp-pointed and compressed ; the teeth behind it are broad and tuber culated. The characters of the sectorial teeth deserve special attention, as, though fundamentally the same 1 The tusks of the Walrus, altogether so aberrant in its dentition, are partial exceptions to this statement, but in old individuals the pulp cavity fills up, and they cease to grow. throughout the suborder, 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 denti tion). It consists essentially of a more or less compressed FIG. llf&amp;gt;. Upper Sectorial Tei th of Carnivora. I, FeJis ; II, Canis ; III, Ursuf.. 1, unteiior, 2, middle, and 3, posterior cusp of blade; 4, inner lobe supported on distinct root; 5, inner lobe, posterior in position, and without distinct root, characteristic of the Ursidx.^ blade supported on two roots and an inner lobe supported by a distinct root (see fig. 116). The blade when fully developed has three cusps (1, 2, and 3), but the anterior is always small, and often absent. The middle lobe is conical, high, and pointed; the posterior lobe has a compressed straight knife-like edge. The inner lobe (4) varies very much in extent, but it is generally placed near the anterior end of the blade, though sometimes it is median in position. 11 FIG 117. Modifications of the lower Sectorlil Tooth in Carnivora. I, Felts ; II, Canis; III, Herpt ste.s ; IV, Lutra; V, Afeles ; VI, Ursus. 1, anterior lobe of blade ; 2, posterior lobe of blade ; 3, inner tubercle ; 4, heel. It will be seen that the relative size of the two roots varies according to the develop ment of the portion of the crown they have respectively to support. In the Ursidse alone both inner lobe and root are wanting, and there is often a small internal and posterior cusp (5) without root. In this aberrant family also the sectorial is relatively to the other teeth much smaller than in the rest of the Carnivora. The lower sectorial (see fig. 117) is the most anterior of the teeth without predecessors in the milk series; it is therefore reckoned the first true molar (m 1). 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 lobes of the blade, of which the hinder (2) is the larger, are separated by a notch, XV. - 55