CRANIAL NERVES OF CHIMERA MONSTROSA. 671 



Skate could be resolved into six nerves (lateralis, intestinal, and four branchials) with 

 six ganglia, thus very materially adding to the discoveries made by Gegenbaur in 

 Hexanchus. Ewart (53) has also made similar statements with regard to Torpedo, 

 which I can further supplement with the observation that in this animal each division 

 of the vagus arises by a separate root and rootlets, amongst which there is only a 

 slight intermingling. In Chimasra, however, the segmentation of the vagus is seen in 

 its most primitive known condition, for each constituent has an obvious ganglion, and 

 an equally obvious separate origin from the brain. One learns, therefore, with some 

 surprise, that the vagus does not exhibit segmentation in its earliest development, the 

 ganglion of vagus 1 only being separate, the others forming a compound mass. 



It seems to the writer that further investigations on the lines followed by Shore (48 

 and 50) are much needed. This author describes ganglion cells in connection with the 

 dorsal branch of the vagus of the Skate, which he believes to be the equivalent of a 

 dorsal root ganglion of a spinal nerve. This can hardly be admitted at present, since 

 there is good reason to believe that the ganglion on the dorsal root is in connection with 

 splanchnic afferent fibres, and this connection is not demonstrated by Shore in the 

 Skate. Further work may nevertheless prove the assumption. Besides discovering the 

 ganglion mentioned above, Shore found that there were ganglion cells in the prse- 

 branchial branches of the vagus. His main conclusions, derived from a study of the 

 sizes of the nerve fibres, are that the " branchial nerves were formed by the separation 

 of the splanchnic rami of some of the anterior spinal nerves from their corresponding 

 somatic rami in relation to the chorclate respiratory system" ; and further that " the 

 branchial ganglia [with the intestinal] are comparable to, and are probably morphologi- 

 cally equivalent to, what Gaskell has called the vertebral or lateral set of ganglia of the 

 sympathetic, and the prse-branchial ganglia are the equivalents in every sense to the 

 pre-vertebral or collateral set of ganglia of the so-called sympathetic system." Shore 

 therefore believes that the vagus of the Skate contains the visceral but not the somatic 

 elements of a spinal nerve, and is a compound, not of several complete segmental 

 nerves, but of the visceral components of the anterior spinal nerves, the corresponding 

 somatic components of which have remained separate. The branchial divisions of the 

 vagus must, hence, be considered secondary developments in connection with the breathing 

 apparatus. It must be obvious to any one who has followed the preceding pages that 

 the bulk of the evidence favours Shore's views ; but whilst we must, at present at 

 any rate, regard the branchial muscles as belonging to the visceral system, it must not 

 be forgotten, as Strong points out (p. 197), that there is a distinction between vaso- 

 motor and branchio-motor fibres, and it is also necessary to emphasise Strong's warning 

 that too much reliance must not be placed upon the size of nerve fibres. Neverthe- 

 less, all studies of adult cranial nerves should, where possible — this, I regret, is not in 

 Cliim&ra — be both anatomical and microscopical, so that results obtained under one 

 section of the work may be checked by those obtained under the other. The sharp 

 distinction drawn by Shore between prse- and post- branchial nerves undoubtedly obtains, 



VOL. XXXVIII. PART III. (NO. 19). 5 A 



