SKELETON AND TEETH 



93 



Fig. 44. — Dentition of Wolf, left side. 

 i.3, third incisor. C, canine, p-l, 

 first premolar, p. 4, fourth premolar. 

 m. 1, first molar. 



number of teeth is usually indefinite and they continue to 

 be shed and replaced, as needed, throughout life ; but in each 

 species of mammal, aside from abnormalities, the number is 

 fixed and constant. Mammalian teeth are very generally 

 divisible into four categories • (1) 

 the incisors, or front teeth, which 

 in the upper jaw are inserted in 

 the premaxillary bones, (2) the 

 canines, or eye-teeth, which are 

 never more than one on each side 

 of each jaw, or four in all, (3) the 

 premolars, called in Man the bi- 

 cuspids, the anterior grinding 

 teeth which have predecessors in the milk-series and (4) the 

 molars, the posterior grinding teeth which have no such pred- 

 ecessors. 



It is customary and convenient to express the numbers and 

 kinds of teeth of a given mammalian species by means of a 

 ''dental formula"; for example, in Man the formula is: 

 ^h ^i, ph ^^h X 2 =32 ; the reason for the multiphcation by 

 two is that the figures deal only with one side of the mouth 

 and must be doubled to give the sum total. Just because, 

 however, the two sides are alike, it is usual to take the doubling 

 for granted. Written out in full, the formula means that Man 

 has two incisors, one canine, two premolars and three molars 

 on each side of each jaw, the horizontal line indicating the 

 division between upper and lower teeth. The number of teeth 

 is frequently not the same in the upper and lower jaws ; for 

 instance, the formula for the Sheep is : i f , c ^, p |, m |, X 2 = 32 ; 

 the total is the same as in Man, but the arrangement is entirely 

 different. The meaning is that in the Sheep there are no upper 

 incisors or canines, but three incisors and a canine are present 

 in each half of the lower jaw, with three premolars and three 

 molars on each side above and below. The Dog gives still 

 another formula : i |, c j, p |, m |, X 2 = 42. What is called the 



