HETERODONTY AND HOMODONTY 



47 



contrary to the prevailing superstition, it is not domestic animals 

 which show the greatest amount of tooth variation. As to special 

 homologies between tooth and tooth, with which we shall deal 

 on a later page, Mr. Bateson has urged almost insuperable 

 difficulties. 



The teeth of the Mammalia are almost without exception 

 " heterodont," i.e. they show differences of structure in different 



p.masc 



s.oc 



oc.co, 



par.oc 



FIG. 34. Skull of Dasyurus (lateral view), al.sph, Alisphenoid ; ang, angular process 

 of mandible ; fr, frontal ; ju, jugal ; Icr, lachrymal ; max, maxilla ; nas, nasal ; 

 oc.cond, occipital condyle ; par, parietal ; par.oc, paroccipital process ; p.max, 

 premaxilla ; s.oc, supraoccipital ; sq, sqnamosal ; sq', z\ gomatic process of squa- 

 mosal. (From Parker a:id Haswell's Zoology.) 



parts of the mouth. As a general rule, teeth can be grouped 

 into cutting incisors, sharp conical canines, and molars, with a 



FIG. 35. Upper and lower teeth of one side of the mouth of a Dolphin (Lagenorhyn- 

 chus), illustrating the homodont type of dentition in a mammal. (After Flower 

 and Lydekker. ) 



surface which is in the majority of cases suited for grinding. In 

 this they contrast with the majority of the lower vertebrates, 

 where the teeth are " homodont " (or, better, homoeodonf), i.e. all 

 more or less similar and not fitted by change of form to perform 

 different duties. But there are exceptions on both sides. In 



