156 Royal Society. 



The whole row of tooth-sacs is i-otitaimnl within a siuti'"' t^oneral 

 connective-t issue iTivestmoiit, which is enlcn-d at tlic lo]) hv the 

 descending process of oral epithelium, whejice the enaniel-gernia 

 are derived. 



As thev attain considerable length, the forming teeth, which 

 were at first vertical, become nearly horizontal, resinning, of course, 

 their upright position once more when they come into place. 



The clue to the whole peculiarity of this arrangement is to be 

 found in the extreme dilatation which the mouth of the snake 

 undergoes. The general capsular investment probably serves to 

 preserve the tooth-sacs from displacement ; while, if the forming 

 teeth remained vertical after they had attained to any considerable 

 length, their points would be protruded through the mucous mem- 

 brane when this was put upon the stretch in the swallowing of 

 prey. 



Just as the author has shown in a previous communication to 

 be the case in the Batrachia and Sauria, the hypothetical " papillary 

 stage " is at no time present. 



From the oral epithelium there extends downwards a process 

 which, passing between and winding around the older tooth-sacs, 

 after pursuing a tortuous course, reaches the furthest and lowest 

 extremity of the area of tooth-development. Here its cfpcal end 

 gives origin to an enamel-organ, and, while it does so, buds forth 

 again beyond it in the form of a c?ecal extremity. Thus at the 

 bottom of this area of tooth-development there is a perpetual 

 formation of fresh enamel-organs, beneath which arise correspond- 

 ing dentine-organs, or papilla?, if such they can be called when 

 arising thus far away from the surface. 



In essential principle, therefore, the formation of a tooth- 

 germ is similar to that already described in mammals aud other 

 reptiles, the difference Iving principally in the enormous relative 

 length of, and the tortuous course pursued by, that inflection of 

 the oral epithelium w hich serves to form the enamel-organs. The 

 attachment of the tooth to the jaw is effected by the rapid de- 

 velopment of a coarse bone, w hich is not deri\ ed from the ossi- 

 fication of the feebly expressed tooth-capsule, but from tissues 

 altogether external to it. Xevertheless this coarse bone of attach- 

 ment adheres more closely to the tooth than to the rest of the jaw, 

 from which, in making sections, it often breaks away. 



The base of the dentinal pulp assists in firmly binding the 

 tooth to this new bone, being converted into a layer of irregular 

 dentine. 



This " bone of attachment " is almost wholly removed and re- 

 newed with the change of each tooth. 



