l6o STRONG. [Vol. X. 



The homologies of this system are in the main clear. The 

 preauditory portion is represented in Urodela by Osborn's 

 '■"J M and /," which divides after its exit, and a part of which he 

 saw proceed forward to the Gasserian ganglion (45, p. 6^, Note). 

 This latter part (7 ?/), passing to the Gasserian ganglion in Cryp- 

 tobranchus, corresponds to the division in the tadpole, which 

 passes forwards dorsad of the Trigeminus and, after passing 

 through its ganglion above the Gasserian ganglion, divides into 

 the infraorbital R. buccalis VII and the supraorbital R. ophthal- 

 micus superficialis VII, together with smaller branches as 

 already described. These supra- and infraorbital branches have 

 been observed in the tadpole by Fischer (20) and Gotte (29), 

 who calls the branch from the VII the radix accessoria. Both 

 investigators correctly surmised their connection with the 

 lateral line system. The ventral division to the R. hyomandi- 

 bularis, however, seems to hai^e hitherto escaped notice in 

 the tadpole. Fischer describes only four and sometimes only 

 three branches from the Gasserian ganglion in Urodela, and 

 these branches include the usual Rr. ophthalmicus, maxillaris 

 and mandibularis of the Trigeminus proper. The fourth 

 branch, in Siredon, extends directly forwards from the dorsal 

 surface of the Gasserian ganglion, dorsad and mesad of the eye 

 to the nasal region. It is cutaneous. This branch is obviously 

 the R. ophthalmicus superficialis and, indeed, Fischer himself 

 conjectures that it is the homologue of the anterior part of the 

 lateral system found in fishes. For the R. buccalis VII and 

 minor twigs of the lateral system we must look among smaller 

 branches from the Gasserian ganglion not noticed especially in 

 Fischer's description, perhaps because bound up with the 

 Trigeminus branches, — a tendency noticeable, as has been 

 seen, in the tadpole. To properly separate these will require 

 microscopic examination. The cause of this difference between 

 the tadpole and urodele forms is probably found in the differ- 

 ent arrangement of the sense organs supplied. In the tadpole 

 they are arranged linearly, in Urodela they appear to be 

 scattered quite irregularly over the head, though exhibiting a 

 tendency to concentration along certain lines. It is possible 

 that the Urodela first pass through the linear arrangement in 

 the course of their development. 



