1883.] NATURAL SCIENCES OF PHILADELPHIA. 181 



(1) The transverse band of fibres (fig. 1) form the greater 

 part of the cerebellum; they appear to arise from columns of 

 fibres in the lateral portions of the medulla, so that they 

 correspond partially to the inferior peduncles of the mammalian 

 cerebellum arising from the restiform bodies. (2) The fine layer 

 of fibres have a direction at right-angles to these, and are three 

 or four deep, seeming to terminate in the lateral portions of the 

 cerebellum, in some cells lying between the cerebellum and the 

 optic lobe. This layer, owing to the peculiar position of the 

 cerebellum beneath the optic lobe, is dorsal to the main transverse 

 band ; if the cerebellum were turned backwards, this layer would 

 be ventral to it. (3) The cells composing the cortex of the 

 cerebellum are of an elongated-oval shape, usually one row, in 

 some places two rows deep. Their greatest diameter is arranged 

 parallel to the main band of transverse fibres. Here, as in other 

 portions of the brain, it was difficult to ascertain whether or no 

 these cells were continued into fibre processes. No such processes 

 were discovered. 



The above account differs widely from that given by Stieda' of 

 the frog's cerebellum ; although the latter is somewhat difficult to 

 understand owing to the lack of figures. 



The 3Iesencephalon. Posteriorly, the mesocoelia is broad and 

 low, and the brain tube has a subpyramidal section ; anteriorly, 

 it becomes more circular and is surrounded by a shield-shaped 

 mass of cells (figs. 2 and 3), surrounded in turn by the mass of 

 longitudinal fibres, the whole constituting the optic lobe and 

 crura. According to Stieda,^ the brain of axolotl has a similar 

 structure in this region. 



The Diencephalon is the most interesting division of the brain; 

 its deep but narrow cavity (diacoelia) is filled with the large 

 choroid plexus ; it has a'ver}^ thin roof and floor, but broad lower 

 sides. The infundihulum is formed b}- the thrusting downward 

 of the posterior portion of the floor. Its walls are much convo- 

 luted; they are composed cliiefly of white matter, with here and 

 there a scattering of nerve-cells, which in some places form a 

 continuous layer. The base of the infundibulum is closely 

 reflected over the pituitary body as a thin lamina. The pituitary 

 body has therefore no communication with the brain cavity, as has 



^ Zeitscbrift fiir wiss. Zcologie, Baud xx. 

 ^ Same Jourual, Band xxv. 



