CRANIAL NERVES IN THE ADULT. 417 



This is taken from a dissection of Scyllium stellare, which like 

 other species has some individualities of its own not found in 

 the other Elasmobranchs. For points not touched on in this 

 description I must refer the reader to the more detailed accounts 

 of my predecessors, amongst whom may specially be mentioned 

 Stannius 1 for Carcharias, Spinax, Raja, Chimaera, &c. ; Gegen- 

 baur 2 for Hexanchus ; Jackson and Clarke 3 for Echinorhinus. 



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 4 : (i) an anterior more 

 or less ventral root; (2) a root slightly behind, but close to the former 6 , 

 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 dis- 

 tance 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 con- 

 nection 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 ophthal- 

 micus 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 coales- 

 cence of two entirely independent branches of the fifth, which unite on 

 leaving the orbit. The dorsalmost of these, or ramus ophthalmicus super- 

 ficialis, 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 posterior 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 joined by the ramus ophthal- 

 inicus 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) 



1 Nervensystetn d. Fische, Rostock, 1849. 



2 Jenaische Zeitschrift, Vol. VI. 



3 Journal of Anatomy and Physiology, Vol. X. 



4 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. pp. 29 and 30. 



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



