146 PROFESSOR MARSHALL. 



4. Teleostei. — The only recorded instances that I can find of devia- 

 tion from the normal arrangement of the eye-muscle nerves among 

 osseous fish are : — 



(a) Amllyopsis, 1 the blind fish of the Mammoth cave of Kentucky, 

 in which the eyes are rudimentary and function! ess, and the eye- 

 muscle nerves, as might be expected, absent. 



(b) Silurus glanis, in which, according to Stannius, 2 the eyes are 

 small, the eye-muscles very slender, and the eye-muscle nerves outside 

 the skull closely united with the ophthalmic branch of the fifth. Stan- 

 nius points out, however, that careful examination shows that all three 

 nerves arise independently from the brain at the normal situations, 

 and expressly notices that, but for the discovery of these extremely 

 slender roots, the eye-muscle nerves of Silurus would have been 

 beyond all doubt described as branches of the fifth nerve. It is of 

 course probable that in the other species of blind fish, whether living 

 in caves, as Typihlichthys, Stygicola, Gronias, Ailia, &c, or living at 

 great Ocean depths, as the Scopelidcv, the eye-muscle nerves are, as in 

 Amblyopsis spelceus, rudimentary or absent; but it will be sufficiently 

 evident, from what has been already said, that neither these blind 

 fish nor such cases as Silurus tell in any way against the independent 

 rank of the eye- muscle nerves. 



5. Dipnoi. — In his account of the African Lepidosiren (Protopterus) 

 anneciens, Professor Owen 8 notices that the optic nerves " are remark- 

 ably small, in correspondence with the feebly-developed organs of 

 vision ; " also that the eye-ball " has no special muscles, whence the 

 absence of the third, fourth and sixth cerebral nerves." 



According to Hyrtl 4 in the South American form, Lepidosiren para- 

 doxes in which also the eyes are very small, the four recti muscles are 

 present, but the two obliqui not represented. The eye-muscle nerves 

 were not found, but were believed to be replaced by two fine branches 

 of the ophthalmic division of the sixth nerve, which branches, how- 

 ever, were not traced into the recti muscles. 



Professor Humphry's 5 description of Lepidosiren {Pvotop>terus) annec- 



1 Noticed by Stannius, Das peripherische Ncrvensystem, p. 18 ; and Schwalbe, loc. cit„ 

 p. 71. 



3 Stannius, op. cit., pp. 18, 19. 



3 Owen, "Description of the Lepidosiren annectens," Trans. Linnwan Soc, vol. xviii., 

 1839, p. 340. 



1 Hyrtl, " Lepidosiren paradoxa," Prag. 1845, p. 44, 



5 Humphry, Observations in Myology, 1872 ; The Muscles of Lepidosiren annectens loith 

 the Cranial Nerves, pp. 77 and 79. 



