MEDIAN SURFACE OF THE BRAIN. 167 



section. It is deep from above down but narrow from side 

 to side. From its under side a prolongation runs down to 

 //, the pituitary body ; behind,, the aqueduct of Sylvius, 

 A, is seen passing back from the third to the fourth ven- 

 tricle, Vq. At FM is the aperture (foramen of Monro) 

 leading into the right lateral ventricle. Crossing the third 

 ventricle and putting the two halves of the fore-brain in 

 direct communication are three small commissures, Coa, 



Cn 



FIG. 69. The right half of the brain as seen on its median side after a section 

 made through the organ in the middle line. Vq, fourth ventricle ; Mo, medulla 

 oblongata ; P, pons Varolii ; II, optic nerve ; H, pituitary body ; Coa, ante- 

 rior commissure ; FM, foramen of Monro leading from the third ventricle, in 

 the cavity of which the lower end of the line SM lies, to the right lateral ven r 

 tricle ; Com, soft commissure, running from side to side of the third ventricle, 

 divided ; Cop, posterior commissure ; Lq, corpora quadrigemina ; A, aque.- 

 duct of Sylvius or iter a tertio ad auartum ventriculum ; Cbl, cerebellum ; 

 Cct'-oci*, corpus callosum; SI, septum lucidum; II 1 , the divided optic com 1 

 missure. 



Com, and Cop, known respectively as the anterior, the 

 median (or soft), and the posterior. The mass seen bound- 

 ing a great part of the side of the third ventricle and 

 united to its fellow by the soft commissure is the optic 

 thalamus. Above the aqueduct is the small median body 

 CV called the pineal gland, which contains no nervous 

 tissue, but has an interest as being, according to Descartes, 



