26 Journal of Comparative Neurology. 



cephalon is separated from the forebrain by a deep depression. 

 It is nevertheless in connection with the pia mater by a mem- 

 branous connective band, or a capsule, which arises from the 

 edges and covers it. The significance of the capsule is not clear. 

 On its upper surface was found a small opening which may have 

 arisen naturally or artificially. The anterior steeply projecting 

 part of the capsule, which in distinction from the rest appears 

 opaque and thick, through a part characterized by its transpar- 

 ent appearance is united with the vascular plexus of the lateral 

 ventricles and is histologically related to them. Up to the time 

 that I had collected newer histological details I was satisfied to 

 consider the organ to be the pineal gland, but after the removal 

 of the membranous capsule I found a stout nodule directed up- 

 ward and lying medially between the mesencephalon and dien- 

 cephalon. 



Henry F. Osborn (^-'83) made the following observations 

 upon the brain of Amphiuma (Muraenopsis). The roof of 

 the diencephalon is of irregular thickness; it is carried forward 

 as a very thin lamina over the pineal gland. The structure of 

 this body is nothing more than a rich plexus of bloodvessels 

 produced from the choroid ; in the apex are numerous fine 

 nuclei, resembling those of connective tissue, certainly not of 

 nerve-tissue. There is no evidence that the latter is present. 

 It will thus be seen that the pineal body is a simple vascular 

 structure, properly speaking, in communication with the brain 

 cavity, since it is apparently surrounded by the brain parietes. 



The same author (64.-88) described the characters of the 

 roof of the diencephalon as very well marked. Just behind the 

 supra-plexus are two oval or round swellings, which represent 

 the ganglia habenarum with distinct median contours, but 

 closely applied to each other in forms in which the supra-com- 

 missure is well developed, such as Menopoma, Amphiuma 

 (Osborn '83 and '84, Fig. 4) and Axolotl (Fig. 1). Arching 

 behind them and spreading beyond, into the thalami is a gray- 

 ish band which probably represents the supra-commissure. This 

 commissure underlies the pineal process, and is not seen upon 

 the surface in Necturus (Figs. 2 and 8), but is apparently pres- 



