ANATOMY OF THE RABBIT. 
By pressing apart the tips of the hemispheres and removing 
the pineal body, the dorsal surface of the thalamencephalon 
will be sufficiently exposed to make out the following 
The slit-like aperture appearing in the middle line after the 
removal of the pineal body represents the dorsal portion of 
the third ventricle (ventriculus tertius) (Fig. 84), the roof 
of which is formed anteriorly by the superficial portion of the 
chorioid plexus (plexus chorioideus), the latter entering the 
274 
features: 
(f) 
ventricle at this point. 
(g) 

Fic. 84. 
The lateral margins of the aperture are largely formed by two 
minute spindle-shaped masses, one on either side, the 
habenulae. Their posterior ends are united by a slender 
transverse band, the habenular commissure (com- 
missura habenularum). The fibres 
ot the commissure are faintly 
traceable forward, where they 
form a pair of thin whitish fila- 
ments (medullary striae). 
The posterior commissure 
(commissura posterior) crosses 
the posterior portion of the roof 
immediately behind and below 
the habenular commissure. 
(h) 
Diagram, showing the 
arrangement of the parts of the 
thalamencephalon as viewed from 
the dorsal surface, after removal of 
the pineal body: a., anterior 
thalamic tubercle; c.h., habenular 
commissure; c¢.p., posterior com- 
missure; c¢.sS., superior colliculus 
(of mesencephalon); g.l. and g.m., 
lateral and medial geniculate bodies; 
h., habenula; m.i., massa inter- 
media; p., pulvinar; v.t., third 
ventricle. 
The walls of the third ventricle 
are formed by the thalami. 
They are broadly connected by 
the intermediate mass (massa 
intermedia), or middle com- 
missure, which may be seen 
from the dorsal surface crossing 
the cavity. 
(j) On either side of the middle line, or of the habenulae, the 
dorsal portion of the thalamus forms a low, somewhat oval 
projection, the pulvinar or posterior tubercle. 
The anterior tubercle of the thalamus is a faint elevation of very 
small dimensions lying in the angle enclosed between the pulvinar and 
the anterior portion of the aperture of the third ventricle. 
