MANATUS. 371 



The coexistence of incisive tusks with molar teeth, and the suc- 

 cessive displacement of the smaller and more simple anterior ones by 

 the advance of larger and more complex grinders into the field of 

 attrition, already, as it were, sketch out characteristics which become 

 normally established and attain their maximum in the Proboscidian 

 family (Elephants and Mastodons) of the Pachydermal order. 



148. Manatus. — The transition from the cetaceous to the 

 pachydermal type of dentition is effected by the Manatee, {Manatus, 

 Scopoli, Cuv.) especially by the modification of the molar series. 



The deflected anterior extremities of the intermaxillary bones 

 each support a single deciduous tusk in the young Manatee (PI. 96, 

 fig. 1, a), but this is not succeeded by a permanent one in either 

 sex. No germs of incisors have been detected in the corresponding 

 part of the lower jaw. The molars of the American Manatee, 

 according to Daubenton and Cuvier(l), are thirty-six in number, nine 

 on each side of both jaws, but they are never simultaneously in 

 place and use. Their crowns in the upper jaw are square, and sup- 

 port two transverse ridges with tri-taberculate summits, having also 

 an interior and posterior basal ridge : each tooth is implanted by 

 three diverging roots, one on the inner and two on the outer side ; 

 they increase in size, very gradually, from the foremost to the last. 

 The crowns of the anterior molars of the lower jaw resemble those 

 above, but the posterior ones have a larger posterior tubercle ; they 

 are all implanted by two fangs, wliich enlarge as they descend 

 and bifurcate at the extremity, PI. 96, fig. 3. 



In the Manatee of Senegal ten molars are developed on each 

 side of both jaws. 



The molars consist of a body of dentine, a coronal covering 

 of enamel and a general investment of cement, very thin upon the 

 crown, and a little thicker upon the fangs. 



All the grinding teeth of the Manatee belong to the true 



(I) Ossemens Fossiles, 4to. vol. v. PI. 1, p. 250. But in the " Regne Animal," Cuvier 

 assigns gzr^ — 32. The number of teeth ordinarily in use at the same time is that represented 

 in PI. 96, fig. 1, where the first molar has been shed and the two last have not come into 

 place : in the lower jaw seven molars are usually in use in the adult : fig. 2 shows the socket 

 of the first which has been shed and the crown of the last, the growth of which is still 

 incomplete. 



B B 2 



