366 HALICORE. 



in the recent specimens, which I have dissected at the Zoological 

 Society, the true deciduous incisors of the upper jaw co-existing 

 with the permanent ones. They are much smaller than the perma- 

 nent tusks of the female, and are loosely inserted by one extremity 

 in conical sockets immediately anterior to those of the permanent 

 tusks, adhering by their opposite ends to the tegumentary gum, 

 which presented no outward indication of their presence. When 

 this gum was stripped off the bone, the deciduous tusks came away 

 with it ; and this may account for their absence in dried crania of 

 immature Dugongs, in which their alveoli are sufficiently conspicuous. 

 The deciduous tusk (PL 92, a) is two inches in length, slightly 

 curved, sub-cylindrical, tapering to both extremities, the fang-end 

 being the smallest; it was perforated, in the specimen figured, by 

 an aperture leading to the extremely contracted cavity in which the 

 remnant of the exhausted matrix was lodged. 



True permanent incisors are not developed in the lower jaw 

 of the Dugong, those which are occasionally found there are 

 abortive remnants of the first or deciduous series, which are not 

 destined at any time to rise above the gum. 



The sloping truncated surface at the anterior part of the lower 

 jaw presents a coarse and loose reticulate structure, and is excavated 

 on each side by four wide irregular sockets. The first is the shal- 

 lowest, the third the deepest. Sir E. Home discovered a small tooth(l) 

 in this socket on each side of the jaw of a young female Dugong. I 

 have also found in the third socket of the left side of the jaw of a 

 full-grown male Dugong, a similar abortive incisor, or rather the 

 fang of an incisor with the crown irregularly eaten away by the 

 absorbent process. This imperfect tooth measured 10| lines in length 

 2^ lines in breadth, and two lines in thickness ; it was slightly bent, 

 with a shallow impression along the middle of the convex side, 

 and with the fang abruptly diminishing to a point at its extre- 

 mity, which was quite closed ; its surface was rougher than in ordi- 

 nary teeth, and presented two or three small vascular perfora- 



says, " It has two incisors in the upper jaw immediately before the two milk-tusks, these are 

 more advanced in the gum than the tusks and, therefore, would appear before them." p. 315. 

 (1) PI. 93, fig. 3. 



