Intracranial Ganglion on Oculomotor Nerve in S. canicula. 553 



may be a contributory cause of a lessened immunity to the organism of 

 disease such as phthisis. 



Our results too confirm the need for caisson workers not to rest during 

 decompression but to take exercise and to breathe deeply so as to secure the 

 escape of nitrogen, which has been dissolved in their body fluid during their 

 work in compressed air. 



On the Occurrence of an Intracranial Ganglion upon the Oculo- 

 motor Nerve in Scyllium canicula, with a Suggestion as to 

 its Bearing upon the Question of the Segmental Value of 

 Certain of the Cranial Nerves. 



By Geo. E. Nicholls, D.Sc, Beit Memorial Fellow (Zoological Department, 



King's College, London). 



(Communicated by Prof. A. Dendy, F.R.S. Eeceived January 21, — Revised 



March 1, 1915.) 



During the study of a number of elasmobranch brains made in connection 

 with my work on Reissner's fibre, I noticed, in a specimen of Scyllium 

 canicula, a collection of ganglion cells upon a length of nerve lying freely 

 beneath the mid-brain. This particular brain had been sectioned in the 

 longitudinal vertical plane and the ganglionic mass occurred at a place which 

 corresponded with the level of the third cranial nerve. Further examination 

 showed that these cells were undoubtedly related to the oculomotor nerve. 

 They are situated upon it in a scattered group which, beginning at a point 

 about 1*4 mm. from the superficial origin of the nerve, stretches to its severed 

 end (roughly 1*6 mm. from its origin). The cells, though only about 15 in 

 number, are moderately large (averaging 20/i x 18/a) and are apparently 

 unipolar or bipolar. Their distribution suggested that other cells of the 

 group must have existed distally to the point of severance of the nerve. 



Upon the opposite side of the brain the corresponding nerve had been cut 

 away quite close to its superficial origin, when the brain was removed from 

 the cranium. 



A second specimen of S. canicula in which some 2 mm. of the third nerve 

 had been left attached to the brain, on either side, showed the ganglion well 

 on both nerves. 



