carpenter: development of the oculomotor nerve. 205 



Neal's limitation of such a phenomenon to anamniote embryos no 

 longer holds. 



Histogenesis of the Neuraxons. As regards the growth and internal 

 differentiation of the neuraxons, my results are in general accordance 

 with those of Vignal ('83), and especially with those of Bardeen (:03), 

 both of whom followed the development of cerebro-spinal nerves in 

 mammalian embryos. The neuroblasts of the oculomotor nidulus send 

 out into the mesenchyme, to form the third nerve, compact homogeneous 

 processes of considerable calibre. These soon break up, apparently by a 

 longitudinal splitting, into fine fibrils ; this differentiation begins at the 

 distal end of the nerve. Bardeen's statement as to the effect of this 

 upon the appearance of a cerebro-spinal mammalian nerve applies 

 equally well to the oculomotor or abducent nerve in the chick. He says 

 (p. 247) : " During the early stages of development these fibrils may 

 either be gathered in small compact groups, each of which represents an 

 axis-cylinder process, or they may be so scattered within the nerve that 

 it is impossible to distinguish definite groups of fibrils corresponding to 

 axis-cylinder processes." The first statement we have seen to be true of 

 the middle portion of the developing oculomotor nerve ; tlie second, of 

 its distal extremity. Bardeen is also of opinion that the fibrils may 

 increase in numbers by longitudinal division. As he has pointed out, 

 these fibrils seem to be of lai-ger calibre than the " primitive " fibrils of 

 Apathy and Bethe occurring in adult neuraxons. According to the 

 observations of Vignal ('83), Gurwitsch (:00) and Bardeen the em- 

 bryonic nerve trunk in mammals becomes invaded by cells which divide 

 the fibrils into small bundles, each of which becomes surrounded by a 

 special envelope (Schwann's sheath) formed by the invading cells. The 

 fibrils making up the bundle are closely bound together in this way into 

 a compact neuraxon. It is possible that the fibrillation of the adult 

 neuraxon may bear some relation to the embryonic fibrils out of which 

 the neuraxon is formed, but the precise nature of this relation remains 

 to be ascertained. 



Nature of the Ciliary Ganglion. The evidence derived from the 

 study of both its development and its histology points to the double 

 nature of the ciliary ganglion of the fowl. I shall now consider, first 

 from an embryological, and then from a histological point of view, the 

 character of the two kinds of elements that enter into the composition 

 of the ganglion. 



We have seen that during development the fundament of the ciliary 

 ganglion receives contributions of cells from the Gasserian ganglion via 



