168 



THE HUMAN BODY. 



which are not markedly intelligent have much convoluted 

 cerebral hemispheres. 



The brain like the spinal cord consists of gray and white 

 nervous matter, but somewhat differently arranged, for while 

 the brain, like the cord, contains gray matter in its interior, 

 a great part of its surface is also covered with it. By the 

 external convolutions of the cerebellum and the cerebral 

 hemispheres the surface over which this gray substance is 

 spread is very much increased (see Fig. 74). 



The Ventricles of the Brain. The minute central canal 

 of the spinal cord is continued into the brain and expands 



FIG. 75. Diagram of the right half of a vertical median section of the brain. 

 Hi H, convoluted inner surface of right cerebral hemisphere; 5, the fifth ventricle; 

 the figure is placed on the thin inner wall of the right lateral ventricle; Cc, cor- 

 pus catlosum; 3, the third ventricle ; the partition separating it from the fifth ven- 

 tricle is the fornix, and just behind the anterior thickened end of the fornix is 

 shown part of the right foramen of Monro m, leading to the right lateral ven- 

 tricle ; t, the soft commissure cut across; in the fore part of the fornix is the 

 anterior commissure; the anterior portion of the floor of the third ventricle 

 shows two downward prolongations, one directed to the optic commissure, z, the 

 other (iiifundibnluni) to the pituitary body, pt; , the pineal body; the thickening 

 immediately beneath its root is the posterior commissure; the mass forming the 

 exposed wall of the ventricle and on which the figure 3 is placed is the inner side 

 of the right optic thalamus ; o, d, the anterior and posterior corpora quadri- 

 ffemina of the right side; 4, the fourth ventricle lying near the dorsal side of the 

 medulla oblongata, Mo, and connected by the tier with the third ventricle; pos- 

 teriorly it is continued to join the central canal of the spinal cord; CV, right crus 

 cerebri; P, pans Varolii; Cb, cerebellum.; where it is divided in the middle line 

 the radial arrangement of its central white matter forming the so-called arbor 

 vitce is seen; op. right optic nerve proceeding from the optic commissure ; oc, the 

 third cranial nerve arising from the crus cerebri; 1, callosal convolution. 



there at several points into chambers known as the ventri- 

 cles. Entering the medulla oblongata it approaches its 

 upper surface and dilates into- the fourth ventricle, 4, Fig. 75, 



