170 MK. F. J. COLE ON THE STEUCTUKE AND MORPHOLOGY OF 



internal svirface of the skull, emerges by a small foramen in the flat proximal portion of 

 the riglit frontal bone, and tlience passes forwards, at some depth from the surfcice, 

 between the cephalic portion of the lateral muscle and the membrane which forms the 

 dorsal boundary of the dorsal (left) orbit. It supplies the skin of the extreme anterior 

 end of the dorsal fin on the upper side. It seems at first sight that this nerve has 

 changed its morphological relations ; for, since it belongs to the right side of the head, 

 we might expect to find its anterior part on the ventral or right side of the interorbital 

 septum, with the right orbito-nasal ; whereas it actually runs on what is morphologically 

 the ventral side of the left eye, crossing in its course the left olfactory and orbito-nasal 

 nerves. But the explanation of this apparent anomaly is not diflicvilt. The dorsal 

 branch of the fifth is a sensory nerve, and was connected in the original symmetrical 

 fish with the skin of the extremity of the dorsal fin, Avhich was originally posterior to 

 the eyes. The fin remained behind the eyes during the rotation of the latter, and after 

 the left eye had travelled round to the right side, the dorsal fin with the neighbouring 

 muscles began to extend forwards. But instead of extending forwards along the now 

 distorted median dorsal line, the fin grew forwards along the edge of the left ectethmoid 

 bone, which supports the left eye in its new position, and which is morphologically 

 ventral to the left eye. The nerve connected with the fin necessarily accouipanied the 

 latter in its growth, and thus the nerve comes to be actually dorsal and morphologically 

 ventral to the left eye. The origin of the nerve remains in its original position, posterior 

 to the eyes on the right side of the skull." It seems to me that this nerve fulfils 

 most of the requirements of the definition of an accessory lateral nerve, and it is 

 interesting to note the light that the peripheral distribution of the cranial nerves 

 throws on the asymmetry of the skull — in the above case supporting Traquair's view of 

 the process. 



Pollard's description of the " reciirrent facial" in Siluroids (1892, i6i) is somewhat 

 open to criticism. In Clarias, he says (p. 529) : — " From a posterior dorsally placed 

 ganglionic extension arises the great Ramus dorsalis recurrens facialis (often wrongly 

 called trigemini) or ' Schadelhohlenast.' It passes upwards intracranially to the 

 parietal bone in which it lies, taking its course directly backwards near the depression 

 in the centre of the parietal. It supplies the mucous canal at the base of the dorsal 

 fin." Again, on p. 533, in Auchejtasjjis : — " The last nerve to be described is the great 

 recurrent branch of the facialis. This stoutest of all the nerves passes upwards and 

 backwai'ds, inclining medianly. In position it arises internally to the anterior semicircidar 

 canal of the ear, and a portion of its ganglion occupies the common space enclosed by 

 cartilage. The nerve runs back into the parietal bone, which it leaves before the 

 posterior end of the cranium is reached. It then takes a deeper course among the body 

 muscles and divides, one portion passing on probably to supply a dorsal canal, thoiigh 

 this was not actually ohserved, while the other becomes closely applied to the first spinal 

 ganglion. No interchange of fibres could be observed, however, and the nerve 

 penetrates the stout bone which runs out to support the shoulder-girdle in Siluroids, 

 and follows a direction towards the pectoral fin. In the parietal, as before mentioned, 

 this recurrent nerce receives the supra-temporal branch from the vagus." (Italics mine.) 

 In Trichomycterus, he remarks (p. 536) : — " This latter nerve [the recurrent facial] gives 



