1883.] NATURAL SCIENCES OF PHILADELPHIA. 119 



size of the cerebellum. This general simplicit}' corresponds to 

 the partial blindness and to the degenerate structure and habits 

 of Amphiiima. 



The Metencephalon is very broad and shallow, with its upper 

 surface divided longitudinally by a central and two slight lateral 

 furrows, and with its borders turning bluntly inwards anteriorl}', 

 apparently to enter the cerebellum. On its lower surface the 

 medulla is divided b^- the central furrow, a continuation of the 

 anterior fissure of the spinal cord. As in other Amphibia, the 

 medulla passes without clear demarkation into the crura cerebri. 



The Epenoephalon. The cerebellum is a narrow, band-like 

 structure, arching across the wide medulla. It is unusually small, 

 and was actually overhung by the optic lobe in my specimens, 

 so as not to be seen in the median line, although this point may 

 require confirmation. The valvula is therefore out of sight, in the 

 dorsal aspect of the brain, but may be seen in the longitudinal 

 sections. 



The Mesencephalon. The optic lobe has no longitudinal 

 furrow, but forms a single, narrow, unpaired body, passing 

 forward into the roof of the Diencephalon without demarkation. 

 TheS'B divisions of the brain cannot be distinguished upon the 

 dorsal surface, but can be seeu in side view by noting the position 

 of the infundibulum below. The Crura (pars peduncularis) form 

 a broad base for the posterior half of the Mesencephalon, which, 

 by an oversight, is not represented in the drawings. As they 

 pass forward, however, they cannot be distinguished from the 

 optic lobe nor from each other, so that this division of the brain 

 forms a cylindrical tube, the component parts of which can onl}- 

 be detected in the microscopic structure. 



Tho,' Diencephalon. The roof of this portion of the brain ter- 

 minates anteriorly in the large pineal gland ; its median surface is 

 marked, in Sfeyiojyoma, by two circular thickenings which were 

 not, noticed in Amphiuma. These ma,y correspond to several 

 structures in the brain roof, which are apparent in the sections. 

 The sides of the Dienoephalon form the thalami, but the promi- 

 nent feature of this portion of the brain is the production of the 

 floor into the long, backward-directed infundibulum, which is best 

 seen in side view. At the base of this process is the large pitui- 

 tary body. At the sides of the infundibulum are two thickenings 

 which converge to enter the thalami ; their relations are clearly 



