carpenter: development of the oculomotor nerve. 167 



opment from one to three or four. The nuclei seen along its course are 

 distinctly peripheral in relation to its fibres. There were no convincing 

 indications of the migration of cells from the neural tube. 



The development of the third nerve in selachians was described by 

 Hoffmann ('99), but he added nothing new to the subject. The nerve 

 in question grows down from the mid-brain and anastomoses with the 

 ganglion ophthalmicus. This is the mesocephalic ganglion of Beard 

 ('87), with whose article the author in the main agrees ; but he con- 

 siders the name ophthalmicus preferable to mesocephalic. Later, the 

 oculomotor nerve and the mesocephalic ganglion draw apart, remaining 

 connected, however, by a ramus anastomoticus. Presently, two ganglia 

 appear on the third nerve, corresponding in position to those described 

 by Schwalbe ('79) for adult selachians. Although the author was not 

 able to work out the development of the ganglionic groups appearing on 

 the oculomotor, he believes the account of Ewart ('90) to be correct, and 

 considers the ciliary the most anterior sympathetic ganglion of the head. 



Allis (:01, p. 131) mentions the presence of small and large cells in 

 the ciliary ganglion of an embryo of Mustelus laevis. The large cells 

 resemble cerebro-spinal ganglion cells, and the author suggests the 

 probability that both spinal and sympathetic elements enter into the 

 composition of the ciliary ganglion. Long and short roots were distin- 

 guished, but no extra-cranial sympathetic root could be made out. 



2. Amphibians. 



Almost nothing is known of the development of the third and sixth 

 cranial nerves and the ciliary ganglion in amphibians. Johnson and 

 Sheldon ('86, p. 94) state that in the embryo newt the oculomotor 

 arises, like certain other of the cranial nerves, as an outgrowth of the 

 neural crest, but no details of the process are given. According to Mar- 

 shall ('93, p. 133) the oculomotor is present as a slender nerve in tad- 

 poles of the frog at the time of the opening of the mouth. It arises 

 from the lower part of the side of the mid-brain, not far from the me- 

 dian plane, and has already the course and relations of the nerve in the 

 adult. Its early development has not been ascertained. 



3. Reptiles. 



Our knowledge of the development of the eye-muscle nerves and the 

 ciliary ganglion in reptiles is derived almost entirely from the extended 

 accounts of the two investigators, Beraneck and Hoffmann, both of whom 

 studied embryos of Lacerta agilis. 



