432 W. H. GASKELL. 



Tracing the nerve in the series of sections, it is easy to see 

 how it at first lies free in among the liver-cells until it reaches 

 the left-hand side of the rounded mass of the right ganglion 

 habenulfB. It then passes along the whole length of this 

 ganglion, lying close against the side of it, successive sections 

 showing that it is becoming less and less superficial, until near 

 the posterior end of the right ganglion habenulse it is lying 

 between the left and right ganglia. It then, still passing deeper 

 and deeper, curves round the posterior border of the right 

 ganglion habenulse just in front of the coramissura pos- 

 terior. From this point it is not easy to trace it further. 

 All the latter part of its course it has been shifting its direction 

 so as to become more and more vertical, and at this point it 

 appears to me to pass straight downwards into the substance 

 of the right ganglion habenulae. 



Ahlborn (3, p. 233) describes the thread-like portion of the 

 epiphysis as a white hair-like thread, which passes from the 

 upper snow-white vesicle (pineal eye) to terminate a little in 

 front of the posterior commissure. He describes it as lying 

 closely over the left ganglion habenulse, and speaks of it as 

 having undergone an unequal obliteration, so that its proximal 

 part has disappeared to such an extent that " die umhullenden 

 Piabliitter meist vollstandig kollabirt sind/' This description 

 he illustrates with fig. 44, PI. xvi, which is a sagittal section 

 through the dorsal eye and the left ganglion habenulce. Now 

 in this very picture it is clear that the nerve has been cut by 

 the section at the spot where he supposes this obliteration of 

 its proximal part to commence, so that in reality the proximal 

 part of the nerve is not in his section at all ; the reason being, 

 as already described, that it clings close to the side of the 

 right ganglion habenulte, and would therefore be found in the 

 sections to the right of the one he has figured. 



As is figured in my sections, the nerve lies free in among the 

 cells of the arachnoid tissue, and passes along the face of the 

 right ganglion habenulae to its posterior border without any 

 sign of connection with either the optic thalamus or the left 

 ganglion habenulas. 



