76 PROFESSOR J. C. EWART ON THE 



The dorsal branch of the trigeminal, like the profundus, neither innervates sensory 

 nor ampullary canals. It may, however, supply some of the taste-buds found in the 

 roof of the mouth of certain fishes. If these taste-buds are modified lateral sense organs, 

 the nerves supplying them are likely to be made up of supra-branchial fibres. 



In Amia it has a similar distribution, but while not connected with canals or pit 

 organs, it supplies a number of surface sense organs, and anteriorly completely fuses with 

 the ophthalmicus profundus. 



While there is no doubt as to the nature of the first two dorsal branches, it is difficult 

 to settle whether the third dorsal branch is represented by one or two nerves — whether 

 the superficial ophthalmic and buccal divisions of the facial together represent a single 

 dorsal branch. This question has been supposed to depend on a still larger question, 

 viz., whether, as suggested by Dohrn (34), there is a hyomandibular segment behind the 

 mouth, and in front of the hyoid. If there are two segments — a hyomandibular and a 

 hyoid — between the mouth and the auditory region, we should expect to find two dorsal 

 nerves. In sharks there are undoubtedly two large nerves, each with a large ganglion, 

 extending forwards one above and one below the eyeball ; but these two nerves may 

 have resulted from the splitting of a single dorsal branch. That this is the case, may be 

 inferred from the fact that the sensory thickening, which in the embryo lies above 

 the hyoid arch, bifurcates and grows forwards over the face. The superficial and 

 ophthalmic branches of the facial, and their related canals (supra- and infra-orbital), are de- 

 veloped in connection with the two forward growths from this sense organ above the hyoid. 



The superficial ophthalmic of the facial {s.o.f., fig. 2) is the first nerve that innervates 

 lateral sense organs. Unlike the profundus and the ophthalmic branch of the trigeminus, 

 it seems to be entirely made up of supra-branchial fibres, i.e., of special sensory somatic 

 fibres. 



Having left the buccal nerve (6k, fig. 2), the facial ophthalmic expands to form a 

 ganglion, and then passes forwards above the contents of the orbit, following more or 

 less closely the supra-orbital canal, all the sense organs of which it supplies. The rest 

 of its fibres reach the superficial ophthalmic group of ampullae (S.O.A., fig. 2). In Amia, 

 this nerve supplies a line of pit organs as well as the supra-orbital canal (S.O., fig. 3). 



The buccal nerve (bu., fig. 2) is at first inseparably connected with the superficial 

 ophthalmic of the facial. In some cases (e.g., Laemargus) it leaves the ophthalmic on the 

 proximal side of the ganglion ; while in others (e.g., Amia) the two ganglia are united 

 at their proximal ends. In other words, the fusion is more complete in some cases than 

 in others ; or, according to the other and more likely view, the splitting is less extensive 

 in Amia than in Lsemargus. The buccal, which like the ophthalmic of the facial, seems 

 to consist entirely of supra-branchial fibres, having left the ophthalmic, at once passes 

 outwards and downwards under the orbit, and divides into two main branches (6k 1 , bu. 2 ), 

 which lie in intimate relation with the maxillary and mandibular divisions of the 

 trigeminal. The buccal supplies (l) the sense organs of the infra-orbital canal, and (2) 

 the inner and outer buccal groups of ampullae. 



