THE NERVOUS SYSTEM 145 



angle of the orbit it turns sharply anteriorly, passing alongside the 

 tooth-bearing, backward extension of the pre-vomer. At a point a 

 little anterior to the level of the optic nerve the palatine nerve passes 

 dorsal to the pre-vomer, between it and the parasphenoid, and runs 

 in a groove on the dorsal side of the former bone. 



At this point, or a little posterior to it, a small twig may remain 

 outside the groove to pass forwards lateral to the palato-nasal artery. 

 This is the lateral palatine nerve (n.pal'. ; Fig. 57). This nerve has not 

 always been found, and in any case it is very fine. Nevertheless even its 

 occasional presence is of interest in view of the condition in Siren, 

 where it normally occurs and fuses with a special branch from the trige- 

 minus nerve (cf. H. W. Norris, 1 9 1 3). In the Salamander it enters the 

 nasal capsule and fuses with a branch coming from the main palatine- 

 profundus anastomosis to form the post choanal nerve (n.p.ch.) (see 

 below). Besides this branch the main palatine nerve gives numerous 

 fine fibres to the mucous epithelium of the palate, which frequently 

 have the appearance of an anastomosing network, and are parti- 

 cularly conspicuous around the palato-nasal artery. 



The main palatine nerve continues along the dorsal side of the 

 pre-vomer, passing between it and the 'Planum internasale', and 

 enters the nasal capsule through the fenestra basalis. Here it is 

 immediately joined by the ventral terminal branch of the ophthal- 

 micus profundus V at the mesial border of the internal narial open- 

 ing. At the junction of these two nerves a fairly conspicuous gang- 

 lion occurs. A number of fine twigs are given off by the combined 

 nerve, most of which pass anteriorly mesial to the internal narial 

 opening, and spread over the roof of the mouth ventral to the olfac- 

 tory epithelium, and ventral to the branches of the olfactory 

 nerve. One branch, however, is given off laterally and passes 

 round the posterior border of the internal nares where it is joined by 

 the lateral palatine nerve — when such is present — to form the post 

 choanal nerve (n.p.ch,). 



No post-palatine nerve, such as occurs in some Urodeles, has 

 been found in the Salamander, and therefore there is no Jacobson's 

 anastomosis. This result is in agreement with those of previous 

 workers (cf. also Coghill's paper on Amblystoma). 



The remainder of the facial nerve, which may now be called the 

 truncus hyomandibularis (n.hy.m.), on entering the antrum petro- 

 sum laterale turns posteriorly and leaves the antrum by its posterior 

 opening, i.e. between the otic and basal processes of the quadrate. 

 Immediately after emerging from the antrum it gives off, antero- 

 mesially: 



