THE RAMUS OPHTHALMICUS PROFUNDUS. 207 



that from these ganglion cells a nerve is given off which 

 accompanies the radix ciliaris longa to the ciliary gan- 

 glion (see Fig. 4). These general cutaneous fibres I ten- 

 tatively homologize with the r. ophthalmicus profundus. 

 They can best be described in connection with the account 

 of the sympathetic nerves which they accompany; their 

 detailed description and the figures illustrating them will, 

 accordingly, be given in the next section. 



The character of these trigeminal fibres in the radix 

 longa of the ciliary ganglion is a matter of great theoreti- 

 cal interest. Van Wijhe, Beard and many others (Mar- 

 shall and Spencer, '81; Ewart, '89 and '93; Piatt, '91; 

 Neal, '98, etc.), as is well known, give in elasmobranchs 

 to the r. ophthalmicus profundus or its embryonic pre- 

 cursor the rank of a separate sensory nerve whose motor 

 part may be represented in the oculomotorius. Or, 

 according to other authors, the motor root of the profundus 

 has disappeared in higher vertebrates, being represented 

 as such in myxinoids. 



Its ganglion ("g. mesocephali ") often has only a tem- 

 porary separate existence and fuses with the Gasserian 

 ganglion in the adult. The suggestion (Schwalbe, '79, 

 and others) that the ciliary ganglion is the vestige of the 

 mesocephalic ganglion is apparently discredited by the 

 accumulating evidence that the former ganglion is com- 

 posed of sympathetic cells only (Retzius, '94 and '94a; 

 Michel, '94; V. Kolliker, '94; Huber, '97). 



The profundus nerve of siluroids, as described by 

 Wright ('84) in Amiurus and by Pollard in Clarias and 

 Trichomycterus ('95) requires further study. Allis thinks 

 in the latter case that it is the r. ophthalmicus superficialis 

 V and not the profundus:, and the same seems to be the 

 case in Amiurus also. 



