90 PROF. MARSHALL AND MR. SPENCER. 



change is seen commencing at stage n (fig. 11, e.g.), where the ganglion 

 has divided into two main portions, one part retaining its original 

 position, whilst the other becomes connected with the nerve N. at 

 some little distance from the third nerve; at stage o-p (figs. 14 and 15) 

 ganglion cells appear to be constantly present at two well-marked 

 points in the course of the third, (1) where the nerve N. is given off, 

 and (2) immediately above the rectus superior. 



At stages k and l (fig. 10) the angle between the nerves N.c. and N. 

 is very considerable, and this increases in the later stages so much 

 that at stage n (fig. 11) the two nerves are almost at right angles to 

 one another; at stages later than this the nerve N~. is much more 

 difficult to define, whilst owing to the close proximity of the third to 

 the fifth nerve it is only with extreme difficulty that the nerve N. c. 

 can be distinguished at all. 



We find, therefore, that the main stem and the branches hi b and 

 in c of stage n become directly the nerves which have the same course 

 and relations in the adult. The ganglion e.g. becomes the ciliary 

 ganglion of the adult 1 . The nerves N. and N.c. become directly 

 continuous with one another, and together form the nerve known as 

 the Ramus ophthalmicus prof undus. The discussion of the morphological 

 import of these two very remarkable nerves we postpone till after the 

 description of the fifth and seventh nerves. 



The Fourth (Pathetic) Nerve. — Concerning the development of the 

 fourth nerve no description has yet appeared, and though our 

 observations do not enable us to give a complete account, still, so 

 far as they go, they are of so definite a character that we think it well 

 to record them here rather than wait for the possibility of completing 

 them at some future time. 



The condition of the fourth nerve at stage n is well shown iu figures 

 11 and 13, of which the former shows the greater part of its course, 

 and the latter its root of origin. The nerve arises' (fig. 13, iv) from 

 the dorsal surface of the extreme hinder border of the mid-brain, so 

 far back indeed that very careful examination is necessary to 

 determine that its origin is really from mid and not from hind- 

 brain. The roots of the two nerves are in close contact on the 

 dorsal surface of the brain. From its root each nerve runs at 



1 Marshall, loc. cit., p. 87, and Schwalbe, "Das Ganglion Oculomotorii," 'Jen. Zeit.,' 

 Bdi xiii, 



