SENSE ORGANS OF AMIURUS. 363 



able chiefly into the outer layers of the tecta optica. The mode in 

 which the fusion of the tori, both with each other and the co7nmissura 

 posterior, is effected at the anterior boundary of the aqvosductus 

 Sylvii, is represented in Fig. 1 4, where their fibres are seen to descend 

 with those of the posterior commissure into the optic thalami. 



At this point the ventricles of the optic lobes die out, and the third 

 ventricle is alone present in frontal sections. In the plane repre- 

 sented in Fig. 15, its cavity is prolonged upwards into a diverticu- 

 lum, the origin of the epiphysis, which makes its way outwards 

 through the roof (Fig. 16) to terminate in the adipose tissue above 

 the roof of the ventriculus communis in the plane of the commissure*, 

 anterior. No prolongation into the cranium such as has been de- 

 scribed especially by Cattie 1 , occurs here, and the wall is quite simi- 

 lar, histologically, to the roof of the ventriculus communis. Immedi- 

 ately in front of the diverticulum of the epiphysis the molecules of 

 the ganglia habenulce make their appearance (Figs. 16 and 17) ; the 

 fibres which collect themselves into the bundles of Meynert soon 

 group themselves into a cylindrical form, and are to be seen on either 

 side close to the walls of the third ventricle at successively lower 

 points (M.B., Figs. 14, 13, 12), till they eventually distribute them- 

 selves, breaking through the strands of the commissura ansulata, to 

 the ganglion interpeduncular e. 



Owing to the fact that the plane which represents the boundary 

 of the primary foi*e-brain and mid-brain is an extremely oblique one, 

 extending from the ganglia habenulos above, downwards and back- 

 wards to the ganglion interpeduncular e, the third ventricle and the ven- 

 tricle of the mid-brain (mesocoele) are to be met with in communi- 

 cation with each other in the same frontal planes (Fig. 11.) In this 

 region the infundibulum communicates below with the hypophysis, 

 and from the ventricle two prolongations ( VLI ) are sent into the 

 lobi inferiores, a shorter inferior cornu, and a longer superior and 

 anterior one, which meet each other at one point, thus partly cut- 

 ting off from the rest of the lobus inferior a somewhat cylindrical 

 lobule. Backwards, the cavity of the infundibulum becomes folded, 

 and is continuous with that of the saccus vasculosus, where all the 

 nervous matter has disappeared with the exception of two cornua 

 somewhat crescentic in section (Fig. 8), round which densely. staining 

 molecules are grouped. 



1 Archives de Biologie. Tome II 

 26 



