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 premaxilla, 

 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 a rule 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 



