622 



THE BRAIN. 



matter lying, as we have said, athwart the diverging crus, in which it is 

 partly imbedded. Its curved median side covered with a thin layer of cen- 

 tral gray matter forms the lateral wall of the third ventricle (Figs. 138, 139, 

 144), and in a longitudinal vertical section of the brain taken in the line of 

 the middle of the third ventricle (Fig. 143, O.T.) is seen occupying the space 

 between the fornix and hind end (splenium) of the corpus callosum above 

 and the diverging crus below. Its more or less straight lateral border abuts 



FIG. 143. 



View of Right Half of Brain of Man as Disclosed by a Longitudinal Section in the Median 

 Line through the Longitudinal Fissure. (Sherrington.) Half natural size. The bulb, seen in 

 longitudinal section at B, passes into thepons, 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 shown in the shaded part marked CR. At GL the central canal of the spinal 

 cord is seen opening out into the fourth ventricle (4th), overhung by the cerebellum (bisected in 

 the middle line), and passing on by the aqueduct beneath the posterior, QP, and anterior, QA, 

 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 quad- 

 rigemina 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 sec- 

 tion of the mesially placed pineal gland 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 

 shown by an unshaded tract. The roof of the third ventricle is seen to be furnished by the arch 

 of the fornix F, shown 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 over- 

 hanging 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 antei-ior pillar /, which is lost to view as it stretches in the lateral wall of the ventricle toward 

 the corpus mammillare 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 OT, 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 pulvinar of the thalamus projecting into the so-called transverse fissure of the 

 brain, shown shaded in the figure, by which the pia mater, passing on beneath the posterior 

 part of the cerebrum and above the cerebellum, gains access to the third ventricle, the position of 

 the velum being shown by the thin black line stretching from the splenium to the fornix. The 

 front (and more ventral) part of the third ventricle is seen to end in the infundibulum, attached 

 to which is the pituitary body H, seen in section at L. In front of the infundibulum is seen the 



