356 THE ANATOMY OF VERTEBRATED ANIMALS. 



brevis, and opponens ; the poUex, an abductor, adductor, flexor 

 brevis, and, perhaps, an opponens. The second, third, and 

 fourth digits have each a pair of flexores breves, which repre- 

 sent the interossei, and are inserted into the bases of the prox- 

 imal phalanges, a relatively large sesamoid being developed 

 in each. Each sends off a fine tendon dorsad to the extensor 

 sheath. The plantaris is large, and, as in the Pig, its tendon 

 passes into the representative of the flsxor brevis digitorum 

 pedis. The tendons of the fl£xor hallucis longus and flexor 

 perforans unite into a common tendon, which subdivides into 

 slips for the digits. 



The dental formula of the Dog is i. j-i-j c. ^j p. m. \^^ 



in. j4^=4:3. The two upper inner incisors, on each side, have 



distinctly trilobed crowns — the lateral cusps of the crown 

 arising from outgrowths of the cingulum at its base. The 

 outer incisor is larger than the others, and its middle cusp is 

 very large, while the outer is rudimentary. The large canine 

 has a strong, curved, pointed crown, with a longitudinal ridge 

 along its posterior face. The crowns of the anterior three 

 premolars are triangular, with a smooth-cutting anterior edge ; 

 the hinder edge is also sharp, but is divided by a notch into 

 two lobes, of which the hinder is the smaller. These teeth 

 are two-fanged. The fourth premolar is a large tooth. In 

 form, its crown has a general similarity to that of the fore- 

 going ; but, firstly, the posterior lobe is relatively much larger, 

 and pointed, so as to form an obvious second cusp ; and, sec- 

 ondly, a strong process of the crown projects inward from its 

 anterior end, and is supported by a distinct fang — so that this 

 premolar is three-fanged. It is termed a carnassial, or secto- 

 rial, tooth, as it bites like a scissors-blade against a corre- 

 sponding tooth in the mandible. The preceding teeth have 

 cutting crowns ; but those of the molars are broad and crush- 

 ing. They exhibit an outer division, formed by two large 

 subequal cusps, and an inner division, also presenting two 

 cusps, the posterior of which is much smaller than the ante- 

 rior. In addition, the cingulum sends up a strong process on 

 the inner side of the crown. 



In the lower jaw, the crowns of the incisors, the outer of 

 which is the largest, are all trilobed. The outer cusp is 

 stronger than the inner in all, and particularly in the outer 

 incisors. The canines resemble those of the upper jaw. Each 

 premolar has two fangs and a sharp triangular crown, the pos- 

 terior edge of which is trilobed, as in the upper premolars; 



