EYE-MUSCLE NERVES IN NECTURUS 155 



About twenty-five animals have been used in this study and 

 the eye-muscle nerves on both sides of twelve of them thoroughly 

 dissected. The rapidity with which the dye in the nerves is 

 oxidised makes impossible the completion of a dissection of the 

 fresh material which involves several hours, so that the dissections 

 were continued after fixation, in a cold solution of ammonium 

 molybdate and the relations of some of the larger structures 

 established after the material was transferred to neutral form- 

 aldehyde. 



The drawings shown in figures 1 and 2 were made from brains 

 of Necturus fixed in formaline-Zenker's fluid, in which neutral 

 formaldehyde (40 per cent) is substituted for the acetic acid 

 ordinarily used with Zenker's fluid. Measurements indicate that 

 this fluid produces in this brain less change in the size, shape 

 and relations of parts than other solutions most often used for 

 the fixation of whole brains. In the brain of Necturus there 

 occurs usually a very slight swelling in the fore-brain (2.5 to 3 

 per cent) ; in the mid-brain and medulla oblongata no marked 

 changes in size due to fixation have been noted after use of this 

 fluid. In the fixation of the brain of Necturus it is essential 

 that the brain be left in the skull and removed after hardening. 

 This is particularly well illustrated by the appearance of the 

 hypothalamus, hypophysis and saccus vasculosus after various 

 treatments (fig. 2). Failure by several authors to recognise the 

 saccus vasculosus in tailed Amphibia has been due evidently to 

 improper conditions during fixation. If the meninges and blood 

 vessels at the caudal end of the hypophysis are cut, the attach- 

 ments of the hypophysis and the saccus vasculosus shrink and 

 shrivel during fixation so that the hypophysis comes to lie ven- 

 tral to the hypothalamus and the lateral dilations of the saccus 

 vasculosus show n(? longer the relations observed in the fresh 

 condition. In order to insure for the fixing fluid ready access 

 to the brain, the part of the parasphenoid bone which forms the 

 floor of the cranium should be removed from the cephalic tip 

 of the hypophysis to the middle of the olfactory tracts. The 

 bone should be left intact over and caudal to the hypophysis. 

 Removal of the roof of the cranium may disturb the attachment 



