152 PROFESSOR MARSHALL 



(d) Siredon. — Fischer 1 has established that the third and fourth 

 nerves are normal in origin and distribution, but was unable to make 

 out anything definite concerning the sixth nerve. 



(e) Crypbobranclms. — Schmidt, Goddard, and V. d. Hoeven are 

 quoted by Hoffmann 2 as stating that in the Cryptobranch the third 

 and fourth are independent nerves, but that the sixth is a branch of 

 the nasal division of the fifth. 



Professor Humphry 3 remarks that the dissection of the cranial 

 nerves is difficult, on account of the "tough areolar tissue of the 

 animal and the numerous accompanying veins." He was unable to 

 " discover the third, fourth or sixth nerves in the orbit." The third 

 and fourth were, however, found in the cranial cavity, but not the sixth. 



Here, again, our information is too imperfect to allow definite conclu- 

 sions to be drawn. If the sixth nerve really appears as a branch of the 

 fifth, it is of importance to note that, as is evident from Professor Hum- 

 phry's figure, the fifth and seventh nerves are quite distinct from one 

 another — a point to which we shall refer when considering the Anura. 



C. Anura. — The condition of the eye-muscle nerves in Anura has 

 been carefully investigated by a number of anatomists, notably by 

 Fischer 4 and Schwalbe. 5 The results of these investigations are as 

 follows : — In all Anura that have been examined, the third and fourth 

 are distinct and independent nerves, with normal origin and distri- 

 bution. In Pelobates and Bombinator the third leaves the skull by 

 the same foramen as the fifth, with which it is in very close contact, 

 though the two nerves are really distinct. 



The sixth nerve in all cases has an independent origin from the 

 brain in the normal position. In Bufo, 6 the sixth nerve preserves its 

 independence along its whole course, and is in all respects perfectly 

 normal. In the other Anura examined — viz. Pipa, liana, Pelobates, 

 Bombinator, and Hyla — the sixth nerve, though arising independently, 

 unites with the Gasserian ganglion, and the branch to the rectus ex- 

 ternus is derived from the " nasal branch " of the fifth. 7 



1 Fischer, Anatomische Abhandlungen iiber die Perennibranchiaten und Derotremen, 

 Hamburg, 1864, p. 127. 



2 Bronn's Thieneich, Bd. vi. 



3 Humphry, Observations in Myology, p. 45, and pi. iv. fig. 22. 



4 Fischer, Amphibiorum nudorum Neurologice specimen primum, pp. 3—22 and 45—48. 

 6 Schwalbe, Das Ganglion Oculomotorii, pp. 28—31. 



Fischer, op. cit., p. 5, and tab. ii fig. 1. 



* Cf. Fischer, op. cit., pp. 3—22, and tab. i. fig. 2 (Hyla), fig. 3 (Bombinator), fig. 4 (Pelo- 

 bates) ; and tab. ii. fig. 1 (Pipa), fig. 4 (Rana) ; also Wyman, Anatomy of the Nervous System 

 of liana pipicns , New York, 1853, pp. 26—28 ; also Wiedershoim in Ecker's Anatomic des 

 Frosches, Zweite Abtheilung, 1881, pp. 20—21. 



