AND TEETH OP THE OPISTHOGLYPHA. 



299 



keeps the tooth attached to the bone, but this hardens when 

 dried, giving the tooth an appearance of being fixed. In order 

 to make a further examination, I mounted the decalcified jaw 

 complete, carefully dissected out from the head of the snake. 

 In text-tig. 1 it will be seen that there are three fixed teeth, 

 while the other two are attached to the socket by means of 

 connective tissue (I), and there is a space, one tooth having 

 dropped out during the process of dissection. I also cut sections 

 of the heads of different genera, taking care to cut the jaw as 

 nearly longitudinally as possible. Externally these hinged 

 teeth difier from the others by being bent more sharply, and also, 

 when moved with a needle, they can be made to bend towards 

 the median line. As regards the forward movement, it is 

 limited to a certain extent. At the base also the two sets of 

 teeth differ from one another by the fact that the hinged teeth 

 have a whitish appearance, due to the presence of the connective 

 tissue which holds it to the bone. In order to study the 



Text-figure 2. 



Tropidonotus stolatus. Longitudinal section of mandible with teeth. X 92. 



mechanism of its movement, I carefully examined the series of 

 sections of the tooth and the bone. Text-fig. 3 shows a diagram 

 drawn from a longitudinal section taken at about the middle of 

 the tooth. It will be noticed that the facets in the maxilla at 

 the base of the two ends of the tooth differ in their structure, 

 and, at the same time, the base of the tooth diflfers markedly at 

 the anterior and posterior ends. In the front the base ends in 

 a peculiar, slightly knob-like structure which also projects 

 inwards. This fact was also noticed by Tomes (13), who writes 

 as follows : — 



" As the tooth approaches completion, there is a 

 peculiarity in the form which its base assumes and which I 

 have not noticed in other animals, namely that the dentine 

 at the widely open base of the tooth is often abruptly bent 

 inwards as though the base of the tooth were about to be 

 closed by a sort of operculum of dentine." 



