On the Development of the Teeth of Ophidia. 155 



That of the frog has an investment, derived in the main from 

 what may be called the accidental condensation of the surrounding 

 connective tissue, which is pushed out of the way as it grows ; 

 while in the lizard the base of the dentine-germ funiishes lateral 

 prolongations, just as has been observed to be the case in man. 



The dentine-organs conform closely with those of mammals ; 

 the odontoblast layer is very distinct, and the processes passing 

 from these cells into the dentine-tubes are often visible. 



The enamel-organs consist only of the outer and inner epithelia, 

 without any stellate intermediate tissue ; as, in some instances, 

 enamel is certainly formed, the existence of the stellate tissue 

 is obviously non-essential. When a tooth is mo\ing to displace 

 its predecessor, its sac travels with it, remaining intact until the 

 actual attachment of the tooth to the bone by ankylosis. 



"On the Structure and Development of the Teeth of Ophidia." 

 By Charles 8. Tomes, M.A. 



Contrary to the opinion expressed by Professor Owen and en- 

 dorsed by Giebel and all subsequent writers, the author finds that 

 there is no cementum upon the teeth of snakes, the tissue \\hich 

 has been so named proving, both from a study of its physical cha- 

 racters and, yet more conclusiAely, from its development, to be 

 enamel. The generalization that the teeth of all reptiles consist 

 of dentine and cement, to which is occasionally added enamel, 

 must hence be abandoned. 



Without as yet pledging himself to the follo\dng opinion, the 

 author belieA'es that in the class of Eeptiles the presence of 

 cementum \vA\ be found associated with the implantation of the 

 teeth in more or less complete sockets, as in the Crocodiles and 

 Ichthyosaurs. 



The tooth-germs of Ophidia consist of a conical dentine-germ, 

 resembling in all save its shape that of other animals, of an 

 enamel-organ, and of a feebly expressed capsule, derived mainly 

 from the condensation of the surrounding c<mnective tissue. 



The enamel-organ consists only of a layer of enamel-cells, 

 forming a very regular columnar epithelium, and of a few com- 

 pressed cells external to this, hardly amounting to a distinct layer ; 

 the enamel-organ is coextensive with the dentine-germ. There is 

 no stellate reticulum separating the outer and inner epithelia of the 

 enamel-organ. 



The successional teeth are very numerous, no less than seven 

 being often seen in a single section ; and their arrangement is 

 peculiar, and quite characteristic of the Ophidia. 



The tooth next in order of succession is to be found at the inner 

 side of the base of the tooth in place, where it lies nearly hori- 

 zontally ; but the others stand more nearly vertically, parallel 

 with the jaw and with the tooth in place, the youngest of the 

 series being at the bottom. 



