THE RABBIT. 375 



Monro, cutting down to the latter : from the 

 middle of this cut take a longitudinal incision 

 backwards through the lyra : press aside the 

 posterior portion of the hemispheres, now com- 

 pletely separated from one another, and make 

 out: 



510. The hippocampal sulcus, a deep, curved groove 

 on the inner face of the temporal lobe, corresponding 

 with the elevation of the hippocampus major. 



511. The velum interpositum, a delicate vascular 

 membrane, continued backwards from the conjoined choroid 

 plexuses, and forming a roof to the third ventricle ( 513). 



512. The optic thalami (o.tk), large masses of mixed 

 grey and white matter, separated in front from the corpora 

 striata by the depression in which the taenia semicircularis 

 lies, and covered dorsally by the velum interpositum. 



513. By removing the velum interpositum the third 

 ventricle (v.$) is exposed ; it is a median vertical fissure, 

 with which the lateral ventricles communicate, anteriorly, 

 by the foramina of Monro. 



514. The anterior commissure (a.co\ a narrow band 

 of white fibres, passing transversely, immediately in front of 

 the' third ventricle, between the corpora striata. 



515. The anterior pillars of the fornix (a.fo\ a 

 pair of delicate, vertical, white bands (cut short by the 

 severance of the body of the fornix), which pass directly 

 downwards immediately posterior to the anterior com- 

 missure. 



516. The middle or soft commissure (m.co), a wide 

 mass of grey matter, passing between the optic thalami 

 nearly level with their dorsal surface, and, in an upper view, 

 almost obliterating the cavity of the third ventricle. 



517. On the upper surface of the hinder half of each 



