VOL. LXXVII.] PHILOSOPHICAL TRANSACTIONS. 323 



terior part of the jaw becoming longer, the number of teeth in that part in- 

 creases, 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 growing 

 with the original ones, as they probably do in most animals. If it be true, that 

 the whale tribe do not shed their teeth, in what way are they supplied with new 

 ones, corresponding in size with the increased size of the jaw ? It would ap- 

 pear 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 degree 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 forwards 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. 



Some genera of this tribe have another mode of catching their food, and re- 

 taining it till swallowed, which is by means of the substance called whalebone. 

 Of this there are 2 kinds known ; one very large, probably from the largest 

 whale yet discovered ; the other from a smaller species. This whalebone, which 

 is placed on the inside of the mouth, and attached to the upper jaw, is one of 

 the most singular circumstances belonging to this species, as they have most 

 other parts in common with quadrupeds. It is a substance, I believe, peculiar to 

 the whale, and of the same nature as horn, which I shall use as a term to ex- 

 press what constitutes hair, nails, claws, feathers, &c. it is wholly composed of 

 animal substance, and extremely elastic* 



Whalebone consists of thin plates of some breadth, and in some of very 

 considerable length, their breadth arid length in some degree corresponding to 

 each other ; and when longest they are commonly the broadest, but not always 

 so. These plates are very different in size in different parts of the same mouth, 

 more especially in the large whalebone whale, whose upper jaw does not pass 

 parallel on the under, but makes an arch, the semidiameter of which is about J- 



* From this it must appear that the term bone is an improper .one.— Orig. 



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