392 



DISSECTION OF THE BABBIT. 



one alone really crosses the cavity of the 

 ventricle. 



The anterior commissure is a small band of 

 transverse nerve-fibres, in the substance of 

 the anterior wall of the ventricle, and 

 immediately in front of the fornix. 



Fig. 69. — Lepus cuniculus. A longitudinal and vertical section 

 brain, taken in the median plane, (a. m. m.) 



A, pituitaiy body. AO, anterior commissure. A.'F, anterior pillar of the 

 fornix, seen in the wall of the third ventricle. C. cerebellum. CA, corpus 

 albicans. CO, corpus callosum. OH, inner surface of left cerebral hemisphere. 

 F, body of the fornix. PM, foramen of Monro. Gr, velum iuterpositum. 

 I, infundibulum. MC, middle commissure. M", anterior optic lobe or ' nates.' 

 O, olfactory lobe. OC, optic cUiasma. OiN", left optic nerve. P, pineal body. 

 PC, posterior commissure. PV, pons Varolii. T, posterior optic lobe, or 

 ' testis.' VA, velum medullse aniicrius, or valve of Vieussens. VP, velum 

 medullsa posterius. 



Ill, third ventricle. IV, fourth ventricle. V, fifth ventricle. 



13. The middle commissure is a very large band 

 of fibres, connecting the two optic thalami 

 across the ventricle. It is nearly circular 

 in outline, and crosses the ventricle about 

 its middle, filling up the greater part 

 of it. 

 y. The posterior commissure is a small band of 

 transverse fibres in the roof of the hinder 



