170 BULLETIN: MUSEUM OF COMPAEATIVE ZOOLOGY. 



cephalad from the Gasserian ganglion, and swelling into a crescentic en- 

 largement near the eye vesicle. This structure is regarded by His as 

 the persistent neural crest in the anterior head region. Both authors, 

 without tracing its fate, assume that the crescentic terminal enlargement 

 is the ciliary ganglion. Kolliker ('79) expresses himself as also of this 

 opinion, although he acknowledges the insufficiency of the evidence on 

 which the assumption is based. That the ganglion in question is the 

 mesocephalic, and not the ciliary of the adult, is beyond doubt. 



The first study of the development of the eye-muscle nerves of verte- 

 brates was made by Marshall ('77, '78) on chick embryos. He found 

 that the neural crest forms, at the twenty-ninth hour of incubation, a 

 prominent outgrowth above the mid-brain. At forty-three hours this 

 outgrowth is directed ventrad and lies in close contact with the walls of 

 the mid-brain ; and at fifty-three hours a large mass of cells is to be 

 found connected with the mid-brain, and about half-way down its side. 

 In a sixty-hours' chick, the oculomotor nerve arises from the ventral 

 surface of the mid-brain, but is farther from the median plane than at 

 later stages. From this evidence the author is " led to the belief that 

 the third nerve is developed directly out of the outgrowth from the top 

 of the mid-brain " seen at the twenty-ninth hour, and " that, at some 

 period between the forty-third and sixtieth hours, its attachment shifts 

 down from the top of the mid-brain to the lower part of its sides " 

 (p. 25). Eabl ('89) accepts, on theoretical grounds, this view of the 

 origin of the third nerve. 



Longitudinal sections of a ninety-six-hours' chick show the oculomotor 

 as a large nerve, arising from the ventral face of the mid-brain. Its 

 base is "ganglionic," and it terminates a little posterior to the optic 

 nerve, in a "ganglionic" swelling. From its enlarged distal end two 

 branches are given off, one passing cephalad and dorsad to the fundament 

 of the posterior rectus muscle, the other continuing the course of the 

 main trunk, crossing the ophthalmic nerve nearly at right angles, and 

 passing caudad and ventrad of the optic nerve. No mention is made of 

 a connection between any part of the third nerve and the ophthalmic 

 division of the fifth. 



In a subsequent paper (Marshall, '81) the author accepts the view 

 advanced by Schwalbe ('79) that this terminal swelling of the trunk of 

 the oculomotor represents the ciliary ganglion of the adult. He ad- 

 vances no opinion as to the source of the cells of the ganglion. 



Marshall's observations on the sixth nerve were incomplete. It was 

 first detected in an embryo of ninety-three hours. Unlike the oculo- 



