4 FRANK E. BEDDARD 



of this tissue. The pecuharly largo extent of this cavity, 

 which will he dealt with immediately, is possihly to be looked 

 upon as a preparation for the subsequent growth of the dental 

 papilla. 



The ingrowths of the epidermis to form the enamel organ, 

 instead of lying within — and firmly embedded therein — the 

 mesoderm tissue underlying the epidermis, depend freely 

 into a spacious cavity just referred to, which forms the tooth 

 follicle. Pouchet and Beauregard figure extensive spaces 

 surrounding these ingrowths, but not to so large an extent as 

 I have found in the young embryos examined by myself. 

 In the lower jaw of my foetus the space invariably commenced 

 immediately below the epidermis ; but in the upper jaw there 

 was frequently a layer of mesoderm immediately underlying 

 the epidermis and perforated by the ingrowth. In other 

 mammals spaces are apt to occur in the same way. The cavities 

 are so large that they are only moulded in the roughest way 

 to the enamel ingrowth ; it is to be remarked, however, that 

 — in the upper jaw at any rate — the labial outgrowths (see 

 Text-figs. 9-12) of the dental lamina, which will be dealt with 

 later, lie in one or two diverticula of this cavity, and in the 

 same way free within it ; they are not closely adpressed to its 

 walls. I imagine that this state of affairs is not altogether 

 natural, Init is due to reagents and consequent shrinkage. 

 I have no means, however, of ascertaining whether any part 

 of this cavity is normal. In any case the practical result is that 

 both in upper and in lower jaw a canal is formed which is quite 

 continuous from one end to the other of both jaws. This 

 cavity gradually narrows at the extreme end of the series of 

 teeth and finally ceases to exist close beneath the epidermis. 

 It is possible that it is associated with the groove which in this 

 and other cetaceans lodges the teeth in the adult animal. 



It is, furthermore, possible that something of the same kind 



led to the erroneous views upon the development of the teeth 



expressed by Goodsir, whose figures persisted until quite 



lately in text-books such as ' Quain's Anatomy '} Here the 



1 Stli 0(1.. vol. ii. 187C, p. 315, lig. 214. 3 and 4. 



