QUADRUPEDS. 207 



number as the jaw lengthens, as in other animals. The 

 posterior part of the jaw becoming larger, the number of 

 teeth in that part increases, the sockets becoming shallower 

 and shallower, and at last being only a slight depression. 



" It would appear that they do not shed their teeth, 

 nor have they new ones formed similar to the old, as is 

 the case with most other quadrupeds, and also with the 

 alligator. I have never been able to detect young teeth 

 under the roots of the old ones ; and, indeed, the situation 

 in which they are first formed, makes it, in some degree, 

 impossible, if the young teeth follow the same rule in grow- 

 ing with the original ones, as they probably do in most 

 animals. 



" If it is true that the whale tribe do not shed their teeth, 

 in what way are they supplied with new ones, correspond- 

 ing in size with the increased size of the jaw ? It would 

 appear, that the jaw, as it increases posteriorly, decays at 

 the symphysis, and while the growth is going on, there is 

 a constant succession of new teeth, by which means the 

 new formed teeth are proportioned to the jaw. The same 

 mode of growth is evident in the elephant, and in some de- 

 gree in many fish ; but in these last, the absorption of the 

 jaw is from the whole of the outside along where the teeth 

 are placed. The depth of the alveoli seems to prove this, 

 being shallow at the back part of the jaw, and becoming 

 deeper towards the middle, where they are the deepest, the 

 teeth there having come to the full size. From this for- 

 wards they are again becoming shallower, the teeth being 

 smaller, the sockets wasting, and at the symphysis there 

 are hardly any sockets at all. This will make the exact 

 number of teeth in any species uncertain *." 



Phil. Trans. 1788, p. 398. 



