THE TEETH OF SIRENIA. 



345 



the disposition of the three structures it recalls the charac- 

 teristics of a Rodent incisor, like which it is worn away 

 obliquely so as to keep a constantly sharp edge, and like 

 which it grows from a persistent pulp. 



In the female, the tusks (incisors) do not project from the 



FIG. 143 ] ). 



gum, their pulp cavities are closed, and the investment of 

 enamel is complete over the crown of the tooth. 



The sloping surface of the upper jaw is opposed by the 

 region of the symphysis of the lower jaw, which is of un- 

 usual depth. In this deflected part of the lower jaw there 

 are eight, or ten (four or five on each side) shallow and 

 rather irregularly-shaped sockets, in which curved distorted 



( ! ) Side view of cranium and lower jaw of a Dugong (Halicore Indicus). 

 From a specimen in the Museum of the Royal College of Surgeons. The 

 surface of the deflected portion of the lower jaw, with its sockets for 

 rudimentary teeth, shown both in front and in profile view, is indicated by 

 the letter a ; the corresponding surface of the upper jaw by the letter I. 



