800 TEETH OF SEALS. 



singular excess of development wliicli tliey manifest in 

 the upper jaw (Fig. 70). In the pinnigracle, as in the 

 plantigrade family of carnivores, we find the teeth which 

 correspond to true molars more numerous than in the 

 digitigrade species, and even occasionally rising to the 

 typical number, three on each side; but this, in the seals, 

 is manifested in the upper, and not, as in the bears, in 

 the lower jaw. The entire molar series usually includes 

 five, rarely six teeth on each side of the upper jaw, and 

 five on each side of the lower jaw, with crowns, which 

 vary little in size or form iu the same individual ; they 

 are supported in some genera, as the eared seals {ptarm\ 

 and elephant seals {cystopliora\ by a single fang ; in other 

 genera by two fangs, which are usually connate in first 

 or second teeth; the fang or fangs of both incisors, ca- 

 nines and molars, are alwaj^s remarkable for their thick- 

 ness, which commonly surpasses the longest diameter of 

 the crown. The crowns are most commonly compressed, 

 conica!"., more or less pointed; in a few of the largest 

 species they are simple and obtuse, and particularly so 

 in the walrus, in which the molar teeth are reduced to a 

 smaller number than in the trae seals. In these, the line 

 of demarcation between the true and false molars is very 

 indefinitely indicated by characters of form or position; 

 but, according to the instances in Avhich a deciduous 

 dentition has been observed, the first three permanent 

 molars in both jaws succeed and displace the same 

 number of milk molars, and are consequently premo- 

 lars; occasionally, in the seals with two-rooted molars, 

 the more simple character of the premolar teeth is 

 manifested by their fangs being connate, and in the 

 Stonorhynchns serridens the more complex character of 



