150 PROFESSOR MARSHALL. 



Fischer's careful descriptions, which have the great advantage of 

 being illustrated by as careful figures, 1 have been referred to by many 

 writers — Stannius, 2 Gegenbaur, 3 Hoffmann, 4 Stieda, 5 <fcc. — who, how- 

 ever, have added nothing to our knowledge on the subject from direct 

 observations of their own. 



Schwalbe, 6 who appears to be the only anatomist since Fischer's 

 time who has directly investigated this interesting point, has fur- 

 nished additional information of great value concerning it. He finds, 

 in confirmation of Fischer's statement, that the nerve to the rectus 

 superior muscle is derived, not from the third nerve, but from the 

 " nasal branch " of the fifth ; but points out that before this nerve is 

 given off the third and nasal nerves cross and lie in very close contact 

 with one another. He considers it probable that at this point there 

 is direct connection between the two, although he was unable to prove 

 it ; and he accordingly supports the view, held also by Fischer and 

 Stannius, that the supply of the rectus superior by the fifth is only 

 apparent and due to the close connection and partial fusion of the 

 third and fifth nerves at this point of crossing. 



Concerning the fourth nerve, Schwalbe's results are more positive, 

 and of great importance. He finds that although in the majority of 

 specimens of Salamanclra maculosa he dissected, the arrangement de- 

 scribed by Fischer obtained, the nerve to the obliquus superior appear- 

 in o- as a branch of the nasal nerve, yet that in some cases, one of which 

 he figures, 7 the fourth may be a completely independent nerve, arising 

 from the brain in the normal position. 



Reviewing, then, these much-quoted cases of Salamandra and Triton, 

 we find that Fischer's account of the anatomical arrangement of the 

 nerve is confirmed by Schwalbe. We find that the sixth nerve is per- 

 fectly independent both at its root and along its whole course — is, in 

 fact, in every way normal. That the fourth nerve is, as a rule, an 

 apparent branch of the " nasal branch " of the fifth, but, at least in 

 Salamandra, may be not uncommonly an independent nerve, normal 

 in every respect. That the third nerve always arises independently 

 from the brain ; that it crosses the " nasal branch " of the fifth, lying 



i Fischer, op. cit., tab. ii., fig. 2 (Salamandra), and fig. 3 (Triton). 



B Stannius, Das periphtrische Nervensystem, p. 19. 



3 Gegenbaur, Hexanchus, p. 549, note 1. 



1 Hoffmann, Brown's Thierreich, Bd. vi, Heft ii, Amphibia, p. 204. 



5 Stieda, loc. cit., p. 174. 



Schwalbe, Das Ganglion Oculomotorii, pp. 25—27. 



7 Schwalbe, Das Ganglion Oculomotorii, Tab. xiii., fig. 13. 



