CARPENTER: DEVELOPMENT OF THE OCULOMOTOR NERVE. 211 



4. The processes of the oculomotor neuroblasts grow out into the 

 mesenchyme as compact neuraxons. After they have attained a con- 

 siderable length they begin to break up, apparently by longitudinal 

 splitting, into fine fibrils. The process of fibril formation seems to be- 

 gin at the free extremity of the nerve and proceed toward the proximal 

 end. As a consequence the whole nerve trunk, especially in its more 

 distal regions, presents the appearance of a large bundle of fine fibrils, 

 among which the fibrils belonging to individual neuraxons cannot with 

 certainty be recognized. 



5. The fundaments of the muscles to which the oculomotor nerve is 

 distributed in the adult appear after the development of the nerve has 

 begun. The last of these muscle fundaments to be differentiated, that 

 of the ventral oblique muscle, is the first with which the third nerve be- 

 comes connected. The branches of the nerve to the dorsal and ventral 

 rectus muscles are developed between the fifth and seventh days of 

 incubation. 



6. The oculomotor nerve in the adult fowl is composed of large and 

 small medullated neuraxons. The majority of the small neuraxons form 

 a peripheral layer along the lateral margin of the nerve, and are contin- 

 ued into the ciliary ganglion. 



II. Ciliary Ganglion. 



1. The fundament of the ciliary ganglion appears during the fourth 

 day as a collection of actively dividing " accompanying " cells near the 

 distal extremity of the oculomotor nerve. There is evidence that these 

 " accompanying " cells are to be regarded as indifferent medullary cells 

 which have migrated into the nerve from the neural tube. During the 

 fifth day nearly all the cells become differentiated into young ganglion 

 cells, characterized by a comparatively large amount of deeply staining, 

 granular cytoplasm, which is accumulated, for the most part, at one side 

 of the rounded nucleus. A few of the indifferent cells do not become 

 ganglionic nervous elements, but assume the characters of elongated sup- 

 porting cells, similar to those which develop the sheaths of Schwann 

 along the trunk of the nerve. These cells may later participate in the 

 formation of the nucleated capsules of the ciliary-ganglion cells. 



2. While the fundament of the ciliary ganglion is undergoing devel- 

 opment, young ganglion cells migrate out from the Gasserian ganglion 

 along the ophthalmic branch of the trigeminal nerve. These cells are 

 characterized by the same deeply staining, granular cytoplasm and 

 rounded eccentric nuclei observable in the ciliary cells, but they are 



