THE SEGMENTAL VALUE OP THE CRANIAL NERVES. 149 



yielded by such cases cannot be accepted as in any way affecting the 

 question of the primitive independence of the eye-muscle nerves. 

 B. Caiidata (Urodela). 

 (a) Proteus. — The specimen of Proteus dissected by Fischer 1 was, like 

 that of Coecilia, too imperfectly preserved to permit him to make any 

 positive statement concerning the eye-muscle nerves ; indeed, he calls 

 attention to and expressly regrets his inability to determine whether 

 these nerves are present or absent. The eyes of this cave-dwelling 

 amphibian are situated beneath the skin, and are of very rudimentary 

 structure, being arrested at what is in other vertebrates a very early 

 embryonic condition. 2 As has been pointed out by Schwalbe, 8 Fischer 

 does not in any way deny the existence of eye-muscle nerves, but 

 merely records his inability to find them in a very imperfectly pre- 

 served specimen. 



(5) Salamanclra and Triton. — I take these two genera somewhat 

 out of their proper zoological order, because they afford perhaps the 

 most widely-known and frequently-quoted examples of abnormal in- 

 nervation of the eye-muscles — instances which must accordingly be 

 carefully considered. 



Fischer, who was the first to draw attention to the point, 4 states 

 that in Salamandra and Triton the third nerve, though rising indepen- 

 dently from the brain, only supplies three of the eye-muscles — the 

 rectus intermis, rectus inferior, and obliquus inferior — the rectus superior 

 receiving a special branch from the " nasal division " of the fifth, 

 which branch is absent in Anura in which the innervation is normal. 

 In discussing the importance of this, he says : — " Quid igitur veri 

 2oossit esse similius, quam quod partium duarum, in quas penes Salaman- 

 drina divisum sit oculomotorius, altera eandem, quam in Ecaudatis 

 retinuerit formam, altera cum Trigemino se conjunxerit ? " The fourth 

 nerve in the same two genera, according to Fischer, u seems to have 

 coalesced with the fifth pair ; " at any rate, he was unable to discover 

 any independent nerve, and the obliquus superior muscle is supplied 

 by the " nasal branch " of the fifth. The sixth nerve is perfectly 

 normal both in its origin and distribution ; it passes very close to the 

 Gasserian ganglion, but is really distinct from it, and leaves the skull 

 by an aperture distinct from that of the fifth. 



1 Fischer, op. eit., pp. 35 and 47. 



2 For a description and figure of the eye of Proteus, vide Semper, Animal Life, Inter 

 national Science Series, pp. 78, 79. 



3 Schwalbe, Das Ganglion Oculomotorii, p. 72. 

 1 Fischer, op. cit., pp. 24, 25, 32, and 47. 



