118 PROF. MARSHALL AND MR. SPENCER. 



This latter nerve (ix b, fig. 12) extends very far forwards in the 

 hyoidean arch, being in this respect very closely imitated by the 

 palatine nerve (vn. pa), so that we are disposed to regard the whole 

 of the mandibular division (vn b) of the seventh, i.e. both palatine 

 and spiracular nerves, as together equivalent to the anterior or 

 hyoidean branch (ix b) of the glossopharyngeal. 



Balfour 1 describes the mandibular branch of the seventh as being 

 large in the embryo, so large, in fact, that he feels difficulty about 

 identifying it with the adult spiracular nerve. His figures, however, 

 show perfectly clearly that what he describes as the mandibular branch 

 of the seventh is really the nerve we have shown to be the buccal. 2 



The maxillary nerve (v b) is, from its time and mode of development, 

 almost certainly to be regarded as the true anterior branch of the 

 fifth corresponding to the mandibular branch of the seventh, although 

 in the absence of a visceral cleft in this region this determination can- 

 not be considered absolutely proved. Whether there is any equivalent 

 branch of the third nerve is very doubtful ; at any rate no such branch 

 can be pointed out with certainty. 



There now remains for consideration the buccal nerve, the deter- 

 mination of which, as a branch of the seventh, is one of the most 

 striking points we have brought to light. Whether this remarkable 

 nerve has any homologue among the branches of the fifth is a point 

 our investigations have not yet enabled us to determine. It is, 

 perhaps, worth while pointing out that there are many points of 

 resemblance between this nerve and the ramus ophthalmicus profundus, 

 points of sufficient importance to render a comparison between the 

 two nerves at any rate a possible and suggestive one. In each case 

 the proximal portion of the nerves in question connects together 

 directly the ganglion of one segmental nerve with that of the nerve 

 next in front, while the distal portion passes forward into the segment 

 anterior to that in which the main branches of the nerve are con- 

 tained. The early origin, the curiously straight course, and the 

 absence of branches until close to their termination, are features 

 common to the two nerves, and ones in which they stand in marked 

 contrast to most other branches. The deep course of the profundus 

 as contrasted with the very superficial one of the buccal nerve may 

 perhaps be attributed to the great development of the eye : in front 



1 Op. cit., p. 202. 



Op, cit., PI. XIV, fig. 2 and fig. 15 a. 



