194 CRANIAL NERVES IN THE ADULT. 



&c. ; Gegenbaur* for Hexanchus ; Jackson and Clarke'' for 

 Echinorliinus. 



The ordinary nomenclature has been employed for the 

 branches of the fifth and seventh nerves, though embryological 

 data to be adduced in the sequel throw serious doubts upon 

 it. Since I am without observations on the origin of the nerves 

 to the muscles of the eyes, all account of these is omitted. 



The fifth nerve arises from the brain by three roots ^: (1) an ante- 

 rior more or less ventral root ; (2) a root slightly behind, but close 

 to the former"*, formed by the coalescence of two distinct strands, one 

 arising from a dorsal part of the medulla, and a second and larger 

 from the ventral; (3) a dorsal and posterior root, in its origin quite 

 distinct and well separated from the other two, and situated slightly 

 behind the dorsal strand of the second root. This root a little way 

 from its attachment becomes enclosed for a short distance in the same 

 sheath as the dorsal part of the second root, and a slight mixture of 

 fibres seems to occur, but the majority of its fibres have no connection 

 with those of the second root. The first and second roots of the fifth 

 appear to me partially to unite, but before their junction the ramus 

 ophthalmicus profundus is given off from the first of them. 



The fifth nerve, according to the usual nomenclature, has three 

 main divisions. The first of these is the ophthalmic. It is formed 

 by the coalescence of two entirely independent branches of the 

 fifth, which unite on leaving the orbit. The dorsalmost of these, 

 or ramus ophthalmicus superficialis, originates from the third and 

 posterior of the roots of the fifth, nearly the whole of which appears 

 to enter into its formation. This root is situated on the dorsal part 

 of the "lobi trigemini," at a point 2?osterior to that of the other roots 

 of the fifth or even of the seventh nerve. The branch itself enters the 

 orbit by a separate foramen, and, keeping on the dorsal side of it, 

 reenters the cartilage at its anterior wall, and is there jomed by the 

 ramus ophthalmicus profundus. This latter nerve arises from the 

 anterior root of the fifth, separately pierces the wall of the orbit, 

 and takes a course slightly ventral to the superior ophthalmic nerve, 

 but does not (as is usual with Elasmobranchs) run below the superior 

 rectus and superior oblique muscles of the eye. The nerve formed 

 by the coalescence of the superficial and deep ophthalmic branches 

 courses a short way below the surface, and supplies the mucous 

 canals of the front of the snout. It is a purely sensory nerve. 

 Strong grounds will be adduced in the sequel for regarding the ramus 

 ophthalmicus superficialis, though not the op)hthalmicus profundus, as 

 in reality a branch of the seventh, and not of the fifth nerve. 



1 Jenaische Zeitschrift, Vol. vi. 



2 Journal of Anatomy and Physiology, Vol. x. 



3 My results with reference to these roots accord exactly, so far as they go, 

 with the more carefully worked out conclusions of Stannius, loc. cit. p. 29 and 30. 



4 The root of the seventh nerve cannot properly be distinguished from this 

 root. 



