SENSE ORGANS OF AMIURUS. 363 
able chiefly into the outer layers of the tecta optica. The mode in 
which the fusion of the tor’, both with each other and the commissura 
posterior, is effected at the anterior boundary of the aqueductus 
Sylvii, is represented in Fig. 14, 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 commissura 
anterior. No prolongation into the cranium such as has been de- 
seribed especially by Cattie!, 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 habenule 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 (7.B., Figs. 14, 13, 12), till they eventually distribute them- 
selves, breaking through the strands of the commissura ansulatu, to 
the ganglion interpedunculare. 
Owing to the fact that the plane which represents the boundary 
of the primary fore-brain and mid-brain is an extremely oblique one, 
extending from the ganglia habenule above, downwards and back- 
wards to the ganglion interpedunculare, 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. !1.) In this 
region the infundibulum communicates below with the hypophysis, 
and from the ventricle two prolongations (VZJ) 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 saceus 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. 
l Archives de Biologie. Tome II 
26 
