CARPENTER: DEVELOPMENT OF THE OCULOMOTOR NERVE. 163 



As this change of position takes place, a nerve — the ophthalmicus pro- 

 fundus — is developed, connecting the mesocephalic ganglion with the 

 branchial sense organ. The oculomotor appears later than the ophthal- 

 micus profundus, and never has any direct connection with the meso- 

 cephalic ganglion, although, during development, it is for a time closely 

 applied to the latter. The true ciliary ganglion is not present until 

 much later. When it does appear, the mesocephalic ganglion and the 

 oculomotor nerve are connected by a small communicating branch, prob- 

 ably corresponding to the radix longa of higlier animals ; and it is near 

 the entrance of this branch into the third nerve that the ciliary 

 ganglion is first to be seen. Beard did not follow the development of 

 the ganglion step by step, but calls attention to the assertion of Hoff- 

 mann ('85), that it aiises in reptiles as an outgrowth of the ophthalmic 

 (mesocephalic) ganglion. He favors the view that it belongs to the 

 sympathetic system. 



Phisalix ('88, '88'^), mistaking the mesocephalic for the ciliary ganglion 

 in skate embryos, asserts that at first the oculomotor nerve and its gan- 

 glion are independent of each other. The ganglion is said to result from 

 the dividing into two of the ganglion of the trigeminal nerve before the 

 oculomotor has appeared. 



Ewart ('90) gives us the first account of actual observations on the de- 

 velopment of the ciliary ganglion in fishes. He finds that, at a certain 

 stage in skate embryos, a slender outgrowth from the inferior border 

 of the ophthalmicus profundus (mesocephalic) ganglion meets and blends 

 with the descending (ventral) branch of the oculomotor. This out- 

 growth is crowded with cells, while the fibres of the descending branch of 

 the oculomotor, as well as its root and trunk, are " absolutely destitute of 

 cells." Later, cells accumulate at the junction between the outgrowth 

 and the oculomotor, as if the intermingling of the two sets of fibres 

 formed a network which resisted the further migration of cells from the 

 mesocephalic ganglion. At a still later stage, in typical cases, all the 

 ganglion cells are seen to have left the outgrowth, and to have accumu- 

 lated on the oculomotor as a rounded mass, from which ciliary nerves 

 take their origin. The ganglion thus arising, plainly the ciliary, stands, 

 therefore, in the relation of a sympathetic ganglion to a dorsal cranial 

 nerve, the ophthalmicus profundus. 



Dohrn ('91) takes up the matter of the histogenesis of the oculomotor 

 more fully than previous writers on the eye-muscle nerves, and also 

 offers an entirely new explanation of the origin of the ciliary ganglion. 

 He observed (p. 3) that in the embryos of selachians the third nerve 



