24 GENERAL ANATOMICAL CHARACTERS 
too much weight to this fact, if it contravenes other reasons for 
determining the homologies of the teeth. The eight remaining 
teeth of the upper jaw offer a natural division, inasmuch as the 
posterior three never have milk-predecessors ; and, although some 
of the anterior teeth may be in the same case, the particular one 
preceding these three always has such a predecessor. These three 
then are grouped apart as the “molars,” or, since some of the teeth 
in front of them often have a molariform character, “true molars.” 
Of the five teeth between the incisors and molars the most anterior, 
or that which is usually situated close behind the premaxillary 
suture, almost always, as soon as any departure takes place from 
the simplest and most homogeneous type, assumes a lengthened 
and pointed form, and is the tooth so developed as to constitute 
the “canine” or “laniary” tooth of the Carnivora, the tusk of the 
Boar, etc. It is customary therefore to call this tooth, whatever 
its size or form, the “canine.” The remaining four are the “ pre- 
molars” or ‘false molars.” This system of nomenclature has been 
objected to as being artificial, and in many cases not descriptive, 
the distinction between premolars and canine especially being 
sometimes not obvious; but the terms are now in such general use, 
and are so practically convenient—especially if, as it is best to do 
in all such cases, we forget their original signification and treat 
them as arbitrary signs—that it is not likely they will be super- 
seded by any that have been proposed as substitutes for them. 
With regard to the lower teeth the difficulties are greater, 
owing to the absence of any suture corresponding to that which 
defines the incisors above; but since the number of the teeth is 
the same, the corresponding teeth are preceded by milk-teeth, and 
in the large majority of cases it is the fourth tooth of the series 
which is modified in the same way as the canine (or fourth tooth) 
of the upper jaw, it is quite reasonable to adopt the same divisions 
as with the upper series, and to call the first three, which are 
implanted in the part of the mandible opposite to the premazxilla, 
the incisors, the next the canine, the next four the premolars, and 
the last three the molars. It may be observed that when the 
mouth is closed, especially when the opposed surfaces of the teeth 
present an irregular outline, the corresponding upper and lower 
teeth are not exactly opposite, otherwise the two series could not 
fit into one another; but as arule the points of the lower teeth 
shut into the interspaces in front of the corresponding teeth of the 
upper jaw. This is seen very distinctly in the canine teeth of the 
Carnivora, and is a useful guide in determining the homologies of 
the teeth of the two jaws. Objections have certainly been made 
to this view, because, in certain rare cases, the tooth which, accord- 
ing to it, would be called the lower canine has the form and 
function of an incisor (as in Ruminants and Lemurs), and on the 
