378 CRANIAL NERVES. 



forks over the cleft in front (spiracle), and supplies the nmiidibular arch 

 (tig. 271 B). This branch forms the prsespiracnlar nerve of the adult, and is 

 homologous with the chorda tympani of Mammalia. Besides however 

 giving rise to this typical branch it gives origin, at a very early period, 

 to two other rather remarkable branches ; one of these, arising from its 

 dorsal anterior border, passes forwards to tlie front part of the head, im- 

 mediately dorsal to the ophthalmic branch of the fifth to be described 

 directly. This nerve is the portio major or superficialis of the nerve 

 usually known as the ramus ophthalmicus supeihcialis in the adult 1 . 



The other branch of the seventh is the palatine branch superficial 

 petrosal of Mammalia the course of which has been more fully investi- 

 gated by Marshall than by myself. He has shewn that it arises ''just 

 below the root of the ophthalmic branch," and "runs downwards and for- 

 wards, lying parallel and immediately superficial to the maxillary branch 

 of the fifth nerve." This branch of the seventh nerve appears to bear the 

 same sort of relation to the superior maxillary branch of the fifth nerve, 

 that the ophthalmic branch of the seventh does to the ophthalmic branch of 

 the fifth. 



Both the root of the seventh and its main branches are gangliated. 



The auditory nerve is probably to be regarded as a specially differen- 

 tiated part of a dorsal branch of the seventh, while the ophthalmic branch 

 may not improbably be a dorsal branch comparable to a dorsal branch of 

 one of the spinal nerves. 



The fifth nerve. Shortly after its development the root of the fifth 

 nerve shifts so as to be attached about half-way down the side of the brain. 

 A large ganglion becomes developed close to the root, which forms the 

 rudiment of the Gasserian ganglion. The main branch of the nerve grows 

 into the mandibular arch (fig. 271 A, F), maintaining towards it similar 

 relations to those of the posterior nerves to their respective arches. 



Two other branches very soon become developed, which were not pro- 

 perly distinguished in my original account. The dorsal one takes a course 

 parallel to the ophthalmic branch of the seventh nerve, and forms, accord- 

 ing to the nomenclature already adopted, the portio profunda of the 

 ophthalmicus superricialis of the adult. 



The second nerve (fig. 271 A) passes forwards, above the mandibular 

 head cavity, and is directed straight towards the eye, near which it meets 

 LI ad tntites ivith the third nerve, where the ciliary ganglion is developed 

 (Marshall). This branch is usually called the ophthalmic branch of the 

 fifth nerve, but Marshall rightly prefers to call it the communicating 

 branch between the fifth and third nerves 3 . 



Later than these two branches there is developed a third branch, passing 

 to the front of the mouth, and forming the superior maxillary branch of 

 the adult (fig. 271 B). 



Of the branches of the fifth nerve the main mandibular branch is 



The two branches of the ramus ophthalmicus superricialis were spoken of as the 

 ram. ophth. superficialis and ram. opth. profundus in my Monograph on Elasmobranch 

 Fishes. The nomenclature hi the text is Schwalbe's, which is probably more correct 

 than mine. 



2 Marshall thinks that this nerve may be the remains of the commissure originally 

 connecting the roots of the third and fifth nerves. This suggestion can only be tested 

 l\v further observations. 



