564 Dr. G. E. Nicholls. Intracranial Ganglion upon the 



It seems to me that the only inference which can safely be drawn from 

 the observed shifting of the ophthalmicus profundus is that its change of 

 relations from the third nerve to the fifth may recapitulate a change which 

 took place comparatively late in the history of the development of the 

 vertebrate head. It does not, however, justify the assertion that the 

 relation of the ophthalmicus profundus to the third nerve was necessarily 

 primary. The mesocephalic neural crest has a considerable antero-posterior 

 extension and other connections between the neural crest and the oculomotor 

 have been observed, anterior to that existing between this nerve and the 

 ophthalmicus profundus. 



That the trigeminus, the ophthalmicus profundus, the eye-muscle nerves, 

 and the nervus thalamicus, should be found related and more or less fused, 

 perhaps shifted, or even become obsolete, is little to be wondered at, occurring 

 as they do in a region where shifting and obliteration of myotomes has, 

 admittedly, been such a marked feature. Nor is it surprising that there 

 remains little or no evidence, in ontogeny, of the primary arrangement in 

 serial independence of the nerves of this region, for the changes which 

 took place in connection with the development of the eye must have been 

 some of the very earliest to disturb the serial arrangement of the nerves. 



In the nerves of the branchial region we have, apparently, a nearly parallel 

 case. There, although we find the several branchial nerves connected from 

 the earliest developmental stages, yet it is generally accepted that these 

 nerves were primarily independent and serially distinct. It is assumed that 

 their displacement and fusion was a feature acquired so early in the develop- 

 ment of the vertebrate head that the prior condition no longer occurs in an 

 abbreviated ontogeny. 



Bearing upon this hypothesis that the ophthalmicus profundus does not 

 represent the dorsal root of a segmental nerve to which the oculomotor 

 would stand merely in the relation of a ventral root, an interesting point 

 may be noted. In certain elasmobranchs, of which Scylliurn is one, the 

 ophthalmicus profundus is said to be little developed* and in the adult 

 to be absent.f It is precisely in Scylliurn, where the oculomotor is found 

 retaining its ganglion, that the encroachment of the ophthalmicus profundus 

 is thus least in evidence. 



As a further objection, the connection of the ciliary ganglion with both the 

 oculomotor and the ophthalmicus profundus nerves might be adduced, on the 

 assumption that this is homologous with the relation, in the spinal region, of 



* Sedgwick, '05, p. 135. 



t Parker and Haswell, '10, vol. 2, p. 161, footnote. 



