14 Field Museum or Natural History — Zoology, Vol. XL 



lary bone just behind the premaxillary suture, or what might 

 be described as at the angle of the front of the jaw, one on each 

 side. 



Premolars: Teeth on side of jaw (maxillary bone), between the 

 canines and the molars. These teeth replace the milk teeth at 

 an early age. 



Molars: The "back teeth," situated immediately behind the pre- 

 molars on side of jaw. These are permanent teeth which are 

 not represented early in life by milk teeth. 



Skull of a Carnivore. Skull of a Rodent. 



(Canines present.) (Canines absent.) 



n. Incisor teeth or incisors; o, canine teeth; p, premolar teeth; r, molar teeth; s, upper carnassial 

 tooth; t, lower carnassial tooth. 



/ Certain forms of teeth are given special names. In carnivorous 

 mammals, for example, the anterior inolar in the lower jaw^ and the 

 posterior premolar in the upper are larger and more prominent than 

 the others and are known as the carnassial (or sectorial) teeth. Those 

 with flattened crowns, from which points or tubercles arise, are called 

 tuberculate teeth, etc. In the Insectivora many of the teeth are of a 

 generalized type, being small, single pointed and showing little err no 

 difference in shape and are known collectively as unicuspid teeth. 

 Further remarks on this subject are unnecessary here, as the more 

 important dental characters are treated under the different families 

 and genera. 



For convenience in describing the dentition the following formula 

 has been adopted by zoologists : — 



I. = incisors, C. = canines, Pm. ^preinolars, M. =inolars. 

 The dental formula of the Virginia Opossum would, therefore, read as 

 follows : 



' rm. ' M. ' 



I- 1 



y_5, Q iZl, 

 4-4' 



50, 



I. -^- 



^"^' o-i 4-4 



the numbers above the line indicating the number of teeth on 

 upper jaw, and those below the line, on the lower. 



the 



