VII 



THE ALIMENTARY TRACT AND ITS 



APPENDAGES, TOGETHER WITH THE SPLEEN 



AND THE MESENTERIES 



THE ALIMENTARY TRACT (PL XXII) 



1. General. 



The alimentary tract and the associated structures of the Salamander 

 show a general similarity to those of the Frog, but there are several 

 noteworthy differences. Of these the following may be mentioned : 

 (i) the presence of teeth on ^o//^ jaws, and the great backward exten- 

 sion of the pre-vomerine teeth ; (ii) the relatively immobile tongue ; 

 (iii) the absence of Eustachian tubes opening into the pharynx; 

 (iv) the fairly simple undivided liver ; (v) the size and shape of the 

 spleen. 



2. The Mouth Cavity. 



Owing to the fact that the outer skin is reflexed some distance 

 dorsalwards at the angles of the mouth over the coronoid process 

 of the lower jaw, there is a difference between the actual gape and 

 the apparent gape. Thus the former extends to about the level of the 

 posterior boundary of the eye, but the latter is continued a short dis- 

 tance behind this. There is only a slight suspicion of free 'lips', but 

 the outer skin covering the jaws is glandular and contains the so- 

 called labial glands. 



The teeth are pleurodont and are directed inwards. They do not 

 terminate in a single point but are bifid at the tips and sometimes 

 tricuspid. There are slight differences in shape between the teeth in 

 the various regions of the mouth, but for practical purposes the 

 dentition may be termed homodont. The teeth are small and occur 

 on both jaws as well as on the pre-vomers. The dentigerous pro- 

 cesses of the latter extend far caudalwards to the back of the mouth, 

 while their S-like shape is characteristic of true Salamanders, and, 

 coupled with the short thick tongue, are definitive of the genus. 



A detailed study of the teeth of Amphibia was undertaken by 

 Hertwig (i 874). He distinguishes two sections of each tooth — the 

 crown which is visible above the gum, and the socket embedded in the 



