II HETERODONTY AND HOMODONTY 47 
contrary to the prevailing superstition, it 1s 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,” ze. they show differences of structure in different 
Fic. 34.—Skull of Dasyurus (lateral view). al.sph, Alisphenoid ; ang, angular process 
of mandible ; fr, frontal; ju, jugal; Jer, lachrymal ; maz, maxilla; nas, nasal ; 
oc.cond, occipital condyle ; par, parietal; par-.oc, paroccipital process ; p.max, 
premaxilla ; s.oc, supraoccipital ; sg, squamosal ; sq’, zygomatic process of squa- 
mosal. (From Parker aid 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, homoeodont), 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 
