No. 2.] 



HISTOGENESIS OF THE RETINA. 



425 



round the nerve. The exact direction of the nerve does not 

 seem to be constant, but, as a rule, it is towards the ventral 

 and median side of the stalk, as indicated in Fig. 9. A sec- 

 tion of the same stage in Necturus is shown in Fig. 10. The 

 whole nerve was struck in one section, and it shows a very 

 large triangular space, partly filled with cells which surround 

 the nerve. 



The idea that the optic nerve arises from the retina and grows 

 to the brain was first advanced by W. Muller ^ although he had 

 no direct observation on which to base his view. The various 

 facts known at his time to histologists and embryologists were, 



Pig_ 10. — Section through the eye of Necturus (i8 mm. long) about the time 

 of hatching. X 100 times. 



however, sufficient basis and his view was finally verified simul- 

 taneously by His 2 and Martin ^ by direct observation in 

 mammalian embryos. The study of the latter is quite com- 

 plete, and in general what I have found in the amphi- 

 bian eye confirms what he found in the cat. He finds 

 also that the optic nerve not only arises from the ganglion 

 cells but also from the cells of the inner nuclear layer. 



1 W. Miiller, Festgabe an C. Ludwig, 1874. 



2 His, His u. Braune's Archiv, 1S90. 



8 Martin, Anatom. Anz., 1890, and Zeit. f. vergl. Augenheilkunde, Bd. 7. 



