180 PROCEEDINGS OF THE ACADEMY OF [1883. 



shown in the sections. In front of the infundibular region the 

 Diencephalon as a whole becomes higher and narrower. There is 

 quite a space between the infundibulum and optic chiasma ; the 

 latter has no clear decussation of fibres as in the frog ; on the other 

 hand, the nerves are given off as two slender fibres on either side 

 of a slightly raised whitish plate. 



The Prosencephalon. The cerebral hemispheres are very long, 

 flattened-oval bodies, narrowing forwards ; they are in close 

 contact, but there is no structural union, except for a short 

 distance in front of the lamina terminalis. The Rhinencephala 

 arise from the outer anterior third of the hemispheres and give off 

 on the lower surface of the brain, the large olfactory nerves. 



Internal and Microscopic Structure. 



The internal structure of the brain, so far as studied, has many 

 interesting features, which may here be considered in connection 

 with the various divisions of the brain tube, concluding with 

 some observations upon the general distribution of the gray and 

 white matter. It must here be said that the minute histology has 

 not been so carefully studied as to afford conclusive data. 



Fig. H represents a longitudinal vertical section of the brain 

 of Amphiuma, magnified four diameters, the shaded portions 

 showing the gray or cellular matter. The vertical lines indicate, 

 approximately, the position of twelve of the thirteen transverse 

 sections which are figured. Fig. 9 passes through the anterior 

 commissure and the forward portion of the diacoelia, not quite 

 agreeing with any vertical line that could be drawn through fig. H. 

 Much enlarged longitudinal and transverse views of the cere- 

 bellum are given in E and F. Fig. G gives an imperfect idea 

 of some of the cells found in the crura. 



The Epencephalon is the only divisioil of the brain which has 

 a complete investment of gray matter ; this statement needs the 

 reservation that the cells surrounding the cerebellum may be of 

 epithelial origin, although this doubt is apparently disproved by 

 the close similarity and continuity of their structure with those of 

 the optic lobe. If this be admitted, the cerebellum is composed 

 of three parts: (1) A continuous band of fibres arching from 

 side to side of the medulla. (2) A fine layer of fibres which 

 have an autero-posterior direction. (3) An investing la3er of 

 cells one or two rows deep. These parts are represented in 

 fig. E, 6, a and c; also in fig. F, h and c. 



