208 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



ing to neither the sympathetic nor cerebro-spinal systems. This concep- 

 tion of the double nature of the ciliary ganglion differs from that of 

 Krause ('81) who, on anatomical grounds, regards the ganglion in mam- 

 mals as mainly sympathetic, but also in part cerebro-spinal. He looks 

 upon the ganglion in vertebrates lower than mammals as a homologue 

 of a spinal ganglion. But in the light of the foregoing observations on 

 its development in the chick, the direct genetic connection of a portion 

 of the ciliary ganglion with the neural crest in vertebrates appears 

 open to question. No embryologist who has distinguished between the 

 ciliary and the mesocephalic ganglia has ascribed to any of the cells 

 of the former a cerebro-spinal origin. 



In birds, as we have seen, only a small proportion of the ciliary cells 

 enter the ganglion from the ophthalmic branch of the trigeminal nerve. 

 But if Hoffmann ('85) has described correctly the development of the 

 ciliary ganglion in Lacerta, it is evident that in reptiles, at least, the 

 greater part of the cells are derived by migration from the Gasserian 

 ganglion. In view of this fact the large number of ganglion cells which, 

 in chick embryos, migrate out along the ophthalmic branch of the fifth 

 nerve, but do not take part in the building of the ciliary ganglion, may 

 possibly possess a phylogenetic significance ; for it is difficult to account 

 for the migration of these short-lived cells into the ophthalmic branch, 

 except upon the supposition that the cells were of functional importance 

 earlier in the history of the race. The majority now fail to reach the 

 ciliary ganglion, and soon disappear. It seems possible that a change 

 in the relative numbers of ciliary cells from the two sources, the Gas- 

 serian ganglion and the neural tube, may have been in some way con- 

 nected with the striking development in birds of the intrinsic muscles of 

 the eye, to which the ciliary nerves are distributed. It is characteristic 

 of the group that these muscles are striated. The radial dilator muscle 

 of the iris is remarkably well developed. The latter organ appears to be 

 under voluntary control (Coues, :03). 



Rubashkin (:03) has recently shown that in the chick certain cells 

 derived from the Gasserian ganglion form, at the extremity of a ramus of 

 the ophthalmic branch of the fifth nerve, a "ganglion olfactorius nervi 

 tricemini." According to his account, these cells do not leave the Gas- 

 serian ganglion before the seventh day of incubation. They are conse- 

 quently not connected with the cells which, much earlier, migrate out 

 along the ophthalmic branch during the development of the fundament 

 of the ciliary ganglion. Many of these, as has been shown, are grouped 

 together in one or more transitory ganglia, which are observable at the 



