466 SYMPATHETIC NERVOUS SYSTEM. 



of these nerves originating as an outgrowth from the central nervous 

 system is no argument in favour of Marshall's view of their nature ; and 

 even if Marshall's opinion that they arise from the neural crest should turn 

 out to be well founded, this fact would not prove their segmental nature, 

 because their origin from this crest would, as indicated in the next 

 paragraph, merely seem to imply that they primitively arose from the 

 lateral borders of the nerve-plate from which the cerebro-spinal tube has 

 been formed. 



Situation of the dorsal roots of the cranial and spinal 

 nerves. The probable explanation of the origin of nerves from the neural 

 crest has already been briefly given (p. 316). It is that the neural crest 

 represents the original lateral borders of the nervous plate, and that, in the 

 mechanical folding of the nervous plate to form the cerebro-spinal canal, its 

 two lateral borders have become approximated in the median dorsal line to 

 form the neural crest. The subsequent shifting of the nerves I am unable 

 to explain, and the meaning of the transient longitudinal commissure 

 connecting the nerves is also unknown. The folding of the neural plate 

 must have extended to the region of the origin of the olfactory nerves, so 

 that, as just stated, there would be no special probability of the olfactory 

 nerves belonging to the same category as the other dorsal nerves from the 

 fact of their springing from the neural crest. 



BIBLIOGRAPHY OF THE PERIPHERAL NERVOUS SYSTEM. 



(351) F. M. Balfour. "On the development of the spinal nerves in Elasmo- 

 branch Fishes." Philosophical Transactions, Vol. CLXVI. 1876; vide also, A mono- 

 graph on the development of Elasmobrancli Fishes. London, 1878, pp. 191 216. 



(352) W. His. " Ueb. d. Anfiinge d. peripherischen Nervensystems." Archiv 

 f. Anat. n. Physiol., 1879. 



(353) A. M. Marshall. " On the early stages of development of the nerves in 

 Birds." Journal of Anat. and Phys.,\o\. xi. 1877. 



(354) A. M. Marshall. "The development of the cranial nerves in the Chick." 

 Quart. J. of Micr. Science, Vol. xvm. 1878. 



(355) A. M. Marshall. "The morphology of the vertebrate olfactory organ." 

 Quart. J. of Micr. Science, Vol. XIX. 1879. 



(356) A. M. Marshall. " On the head-cavities and associated nerves in Elasmo- 

 branchs." Quart. J. of Micr. Science, Vol. xxi. iSSi. 



(357) C. Schwalbe. "Das Ganglion oculomotorii. " Jenaischc ZeitscJtrift, 

 Vol. xin. 1879. 



Sympathetic nervous system. 



The discovery that the spinal and cranial nerves together 

 with their ganglia were formed from the epiblast was shortly 

 afterwards extended to the sympathetic nervous system, which 

 has now been shewn to arise in connection with the spinal and 



