XTII 



PHYLUM CHORDATA 



551 



In the Manatee there are two rudimentary incisors on each side, 

 both in the upper and the lower jaw ; these disappear before 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 transvers 

 ridges, and are preceded by milk- 

 teeth. In the Dugong there are no 

 incisors in the mandible of the adult, 

 and only 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 mandible, and also a rudimen- 

 tary second pair in the tipper 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. 1209) 

 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 carnas- 

 sials, consisting of the last pre-molar 

 in the upper and the first molar in 

 the lower jaw. is universal. In front of the carnassial the teeth 

 are compressed and pointed ; behind it they have broad surfaces. 

 In the Cat family (Felidce) the formula is 



.31 3 1 

 t. 3, c. p p. g, m. l 



The lower carnassial is thus the last of the series. 

 (Canidae) the formula is usually 



.3 1" 4 2 



i. y c. - r p. ^ m. ^ = 42, 



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



3 

 In the Pinnipedia there are always fewer than ^ incisors, and 



o 



caruassials are not developed. The pre-molars and molars have a 



FIG. 1208. Section of upper jaw of 

 Balsenoptera (a), with baleen- 

 plates (6, c) frayed out at their free 

 edges (d, e). (After Owen.) 



In the Dogs 



