460 CRANIAL NERVES. 



The other branch of the seventh is the palatine branch superficial 

 petrosal of Mammalia the course of which has been more fully investigated 

 by Marshall than by myself. He has shewn that it arises "just below the 

 root of the ophthalmic branch," and " runs downwards and forwards, 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, V), 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 

 properly distinguished in my original account. The dorsal one takes a 

 course parallel to the ophthalmic branch of the seventh nerve, and forms, 

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

 ophthalmicus superficialis 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 

 and unites with 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 1 . 



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 

 obviously comparable to the main branch of the posterior nerves. The 

 superficial ophthalmic branch is clearly equivalent to the ophthalmic branch 

 of the seventh. The superior maxillary is usually held to be equivalent to 

 that branch of the posterior nerves which forms the anterior limb of the fork 

 over a cleft. The similarity between the course of this nerve and that 

 of the palatine branch of the seventh, resembling as it does the similar 

 course of the ophthalmic branches of the two nerves, suggests that it may 

 perhaps really be the homologue of the palatine branch of the seventh, there 



1 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 

 by further observations. 



