The Vertebrate Skeleton

by Sidney H. Reynolds

They are divisible into four distinct groups, the incisors, canines, premolars and molars. There are three incisors, one canine and four premolars on each side of each jaw. But while there are three molars on each side of the lower jaw, the last is wanting in the upper jaw. The dentition of the dog may then be represented by the formula

i ³/₃ c ¹/₁ pm ⁴/₄ m ²/₃ × 2 = 42.

In each jaw there is one large specially modified tooth called the carnassial, the teeth in front of this are more or less pointed and compressed, while those behind it are more or less flattened and tuberculated.

Teeth of the upper jaw.

The first and second incisors are small teeth with long conical roots and somewhat chisel-shaped crowns. Surrounding the base of the crown there is a rather prominent ridge, terminated laterally by a pair of small cusps. This ridge, the cingulum, serves to protect the edge of the gums from injury by the hard parts of food. The third incisor is a good deal like the others but larger, and has the cingulum well developed though not terminated by lateral cusps. All the incisors are borne by the premaxillae, the remaining teeth by the maxillae.

The canine is a large pointed tooth, slightly recurved and with a long tapering root.

The premolars are four in number, and in all the cingulum is fairly well seen. The first is a very small tooth with a single tapering root, the second and third are larger and have two roots, while the fourth, the carnassial, is much the largest and has three roots. Each of the second, third and fourth premolars has a stout blade, the middle portion of which is drawn out into a prominent cone; the posterior part of the fourth premolar forms a compressed ridge, and at the antero-internal edge of the tooth there is a small inner tubercle.

The two molar teeth are of very unequal size. The first, which has two anterior roots and one posterior, is wider than it is long, its outer portion being produced into two prominent cusps, while its inner portion is depressed. The second molar is a small tooth resembling the first in its general appearance, but with much smaller outer cusps.

Teeth of the lower jaw.

The three incisors of the lower jaw have much the same character as the first two of the upper jaw; while the canine is identical in character with that of the upper jaw.