carpenter: development of the oculomotor nerve. 159 



into this region of fine, very slightly medullated neuraxons from a 

 gaugliated dorsal nerve, the ophthalmic branch of the trigeminus. 

 These neuraxons are identical in appearance with those of a typical 

 ramus communicans passing, in the thoracic region of the fowl, to a 

 sympathetic ganglion. A lack uf correspondence between this portion 

 of the ciliary ganglion and a typical sympathetic ganglion is to be 

 recognized, however, in the comparative absence of medullation around 

 the fine ciliary neuraxons given off distally. The post-ganglionic 

 neuraxons of a sympathetic ganglion are also of small calibre, but in 

 the hen they are well medullated. This lack of correspondence, due 

 merely to differences in the degree of medullation, seems comparatively 

 unimportant. It should be remembered, too, that in other classes of 

 vertebrates non-medullated neuraxons are characteristic of post-ganglionic 

 sympathetic nerves. 



PART II. - DEVELOPMENT. 

 A. Historical Survey. 



In reviewing the literature which deals with the development of the 

 ciliary ganglion, it must be kept in mind that the name " ciliary " has 

 been applied by various authors to two entirely distinct ganglia. One 

 of these is found at the base of the first or ophthalmic branch of the 

 trigeminal nerve, while the other is connected with the oculomotor 

 nerve, and is the true ciliary ganglion of the adult. 



The first of these ganglia arises in the following manner. In early 

 stages of development, at least in sharks and birds, the most anterior 

 portion of the neural crest becomes differentiated, in the region of the 

 eye muscles, into an enlargement resembling the fundament of a cerebro- 

 spinal ganglion. In sharks this has been observed to fuse later with 

 the anterior part of the Gasserian ganglion, and the same fusion doubt- 

 less takes place in birds. From the ganglion originating thus, the first 

 branch of the trigeminus proceeds forward (van Wijhe, '82 ; Beard, '87 ; 

 Neal, '98). For this ganglion of the ophthalmicus profundus in sharks 

 Beard, in 1887, proposed the name " mesocephalic." Following Dohrn 

 and Neal, I have adopted this designation, since all names previously 

 applied to the ganglion in question have been used as synonyms for the 

 ciliary. Indeed, as already stated, the name ciliary itself has often 

 been applied to it. 



The separate development of the ganglion of the ophthalmic branch 

 of the trigeminus, and its subsequent fusion with the rest of the 



