536 



ZOOLOGY 



SECT. 



dentition; in Rhytina teeth were absent. In the two former 

 Sirenians there are incisors and molars with a wide diastema be- 

 tween them. In the Manatee there are two rudimentary incisors 



on each side, both in the upper and 

 the lower jaw; these disappear be- 

 fore the adult condition is reached. 

 There are altogether eleven molars 

 on each side above and below, but 

 not more than six of these are in 

 use at once, the more anterior when 

 worn out being succeeded by the 

 more posterior. They have enamelled 

 crowns with transverse ridges, and 

 are preceded by milk teeth. In the 

 Dugong there are no incisors in the 

 mandible of the adult, but one tusk- 

 like pair in the upper jaw, large in 

 the male, in which they grow from 

 persistent pulps, little developed in 

 the female, and remaining concealed 

 in their sockets. In the young there 

 are rudimentary incisors in the man- 

 dible, and also a rudimentary second 

 pair in the upper jaw. There are 

 either five or six molars on each side, 

 both in the upper and lower jaws. 

 These are cylindrical teeth, devoid 

 of enamel, and with persistent 

 pulps. 



In the Carnivora vera (Fig. 

 1128) the dentition is complete, 



heterodont and diphyodont, and all the teeth are provided with' 

 roots. The incisors are relatively small, chisel-shaped teeth ; there 

 are nearly always three of them on each side, in both upper and 

 lower jaws. The canines are always large and pointed. The 

 presence of carnassials, consisting of the last pre-molar in the upper, 

 and the first molar in the lower, jaw, is universal. In front of this 

 the teeth are compressed and pointed ; behind it they have broad 

 tuberculated surfaces. In the Cat family (Felidce) the formula is 

 .313 1 



FIG. 1127. Section of tipper jaw, with 

 baleen-plates, of Balsenoptera, 

 (After Owen.) 



The lower carnassial is thus the last of the series.' In the Dogs 

 (Canidae) the formula is usually 



.31 4 2 



and in the Bears (Ursidse) it is the same. 



