CHAP, ii.] 



979 



FIG. 120. VIEW OF EIGHT HALF OF BRAIN OF MAN, AS DISCLOSED BY A LONGI- 

 TUDINAL SECTION IN THE MEDIAN LINE THROUGH THE LONGITUDINAL FISSURE. 

 (Half natural size.) (Sherrington.) 



The bulb, seen in longitudinal section at B, passes into the pons P, and into the 

 crus cerebri, which last is cut obliquely across as it diverges into the hemisphere 

 and passes out of the section. A part of the ventral surface of the crus is 

 shewn in the shaded part marked C.R. At GL the central canal of the spinal 

 cord is seen opening out into the fourth ventricle (4th) overhung by the cere- 

 bellum (bisected in the middle line), and passing on by the aqueduct beneath the 

 posterior, Q.P, and anterior, Q.A, corpora quadrigemina into the third ventricle 

 (3). The posterior corpus quadrigeminum is continuous behind with the valve 

 of Vieussens, attached to the superior peduncle of the cerebellum, and seen in 

 a longitudinal section overhanging the front part of the fourth ventricle. The 

 corpora quadrigemina appear relatively small because the section passes in the 

 median line in the depression between the right and left bodies of the two 

 pairs ; and immediately in front of them is the section of the mesially placed 

 pineal fjland P, which overhangs the opening of the aqueduct into the third 

 ventricle, and the right arm of which running in the lateral wall of the third 

 ventricle is shewn by an unshaded tract. 



The roof of the third ventricle is seen to be furnished by the arch of the fornix F, shewn 

 unshaded in longitudinal section. Posteriorly the body of the fornix passes 

 into the diverging right posterior pillar, where F is shaded, and is lost to view 

 under the overhanging rounded hind end or splenium Sp. of the corpus callosum. 

 In front the body of the fornix is seen passing just behind the transverse section 

 of the anterior commissure A, into the diverging right anterior pillar, f, which 

 is lost to view as it stretches in the lateral wall of the ventricle towards the 

 corpus mammiUare or albicans M. The small white cross immediately behind 

 /, indicates the position of the foramen of Monro. The bulging median surface 

 of the optic thalamus, O.T, is seen forming the lateral wall of the hinder (and, 

 owing to the cranial flexure, the more dorsal) part of the third ventricle, and 

 on this below the area of the pineal gland is seen, unshaded, the section of 

 the soft or middle commissure C. Between the pineal gland (P) and the 

 splenium Sp, is seen the hind end or pulvhtar of the thalamus projecting into 



