440 MR. C, H. O DONOGHUE ON THE 
the main trunk, just before joining which it receives the other 
tributary coming from the prosencephalon. 
The ventral factor collects blood from the lower surface of the 
prosencephalon and diencephalon as far back as the optic chiasma 
and passes dorsally into the main vein. The third factor isa 
posterior one that passes behind the edge of the prosencephalon 
to anastomose with its fellow. In the middle line this vessel 
receives a vein from the optic lobes and a large number of 
smaller ones from the anterior choroid plexus roofing the third 
ventricle. 
Text-figure 2. 
AC. 
Ach, 
Pch 
PC. 
LM. 
Sketch of the dorsal side of the brain of Scylliwm canicula, showing the 
arrangement of the anterior and posterior cerebral veins. 
For explanation of lettering see p. 454. 
l.iv. The Inter-Orbital Vein [Pls. I & II., 1.0.] is a small but 
well-marked vein running from one orbit to the other in a canal 
in the basi-cranial cartilage, and it enters the orbit towards its 
posterior end just in front of and slightly below the large 
