THE CRANIAL NERVES OP SCYLLIUM. 117 



is clearly the nasal nerve of Mammalia, is a primitive and very con- 

 stant nerve, and that it never shifts its position so as to lie dorsal to 

 all the eye muscles, as supposed by Balfour. 



The two divisions of the ophthalmicus superficialis, on the other 

 hand, appear to be very variable indeed in different Vertebrates; 

 they attain their maximum development in the Elasmobranchs, pro- 

 bably on account of the great development and importance of the 

 organs they supply — the mucous canals. In Mammalia the ophthalmic 

 branch of the fifth is represented by the frontal and lachrymal nerves, 

 while the seventh nerve has no ophthalmic branch. 



It would hardly be profitable to discuss the various descriptions of 

 these nerves by different writers ; we will merely point out here that 

 Schwalbe 1 clearly distinguishes the three ophthalmic nerves. He calls, 

 as we have done, the ophthalmic branches of the seventh and fifth 

 nerves together the ramus ophthalmicus superficialis, distinguishing the 

 component parts as portio major (vn a) and portio minor (v a) respec- 

 tively. He also employs the term ramus ophthalmicus profundtos in the 

 same sense as we have done. Balfour, who was the first to clearly 

 recognise the double nature of the ophthalmicus superficialis, is in error 

 in calling the lower portion of it (v a) the ophthalmicus profundus. 



Concerning the other branches of the nerves in question, there can 

 be little doubt that the hyoidean branch (vii c) of the seventh and the 

 mandibular branch (v c) of the fifth are homologous nerves, supplying 

 respectively the anterior walls of the hyoidean and mandibular arches ; 

 and there appear to be good reasons for viewing the nerve (in c) as the 

 corresponding branch of the third. 2 All the three nerves in question 

 are either mainly or exclusively motor in function. 



The seventh, like the hinder cranial nerves, forks over a visceral 

 cleft — the spiracle. As shown in figs. 11 and 12, there are two 

 branches of the seventh which run down in front of the spiracular 

 cleft, viz., the buccal (vii d) and the mandibular (vii b), which latter 

 divides almost at once into the palatine and spiracular nerves. The 

 history of their development and a comparison of the branches of 

 the seventh with those of the glossopharyngeal (ix. fig. 12), leave no 

 possible room for doubt that of these the mandibular branch (vn b) is 

 the homologue of the anterior branch (ix b) of the glossopharyngeal. 



1 " Das Ganglion Oculomotorius," ' Jenaische Zeitschrif I,' Bd. xiii., pp. 11 seq. 

 s Marshall, loc. cit., p. 88. 



