MUSTELUS L^VIS. 203 



there gradually disappears, numerous branches being sent 

 toward the adjacent mucous lining membrane of the mouth 

 cavity. In the terminal part of its course it lies quite close 

 to the terminal portion of that branch of the ramus palatinus 

 that Grreen considers as the homologue of the chorda tympani. 

 This part of the truncus facialis of Mustelus is thus the ramus 

 mandibularis internus s. profundus of Stannius, and it is the 

 nerve that Ruge (55) and many others homologise with the 

 chorda tympani of man. Whether it be or be not that nerve 

 depends on whether the chorda is a post- or pre-spiracular 

 nerve. 



Review and Comparison of the Ophthalmic Nerves. 



There is, as is only too well known, much confusion in the 

 descriptions of, and more particularly in the nomenclature 

 relating to, the ophthalmic nerves of fishes. This is often so 

 misleading that I venture to give, before discussing the 

 nerves, an explanation of the manner in which it seems to 

 have arisen. 



Stannius (59, p. 34) included all the ophthalmic nerves of 

 fishes under the name ramus primus n. trigemini s. ophthal- 

 micus, a name which, shortened to Trigeminus I, is even still 

 retained by certain authors. Stannius says that the nerve 

 thus defined by him is always Avholly sensory, excepting in 

 the Cyclostomata, and that it is formed by the union of two 

 bundles of fibres, one derived from an anterior trigeminal 

 root and the other from a posterior one. In certain teleosts, 

 he says that the ramus ophthalmicus is found as a single 

 trunk Avhich runs forward, near the roof of the orbit, dorsal 

 to all the muscles of the eyeball. In other teleosts, and in 

 all the Plagiostomata, the nerve is said to be represented by 

 two branches which sooner or later unite, more or less com- 

 pletely, to form a single trunk. In these latter teleosts both 

 branches of the nerve are said to have the course of the 

 sinffle trunk in the first-mentioned ones, while in all the 



