STRUCTURE OP THE ENCEPHALOtf, 



195 



may be termed collectively the epencephalon (Owen), occupy 

 an inferior compartment in the back part of the cranium; the 

 cerebellum being roofed in 

 and separated from the rest 

 of the brain above it by a 

 septum of dura mater 

 called the tentorium cere- 

 belli, which in some ani- 

 mals, as the cat, even 

 contains a lamina of 

 bone. 



145. The whole of the 

 brain above the level of 

 the tentorium is included 

 under the name of cere- 

 brum, and is connected 

 with the parts below by a 

 neck or isthmus, in thick- Fig. 100. MESIAL SECTION or BRAIN. 

 ness about the size of a Medulla oblongata ; 6, , pons Va- 

 n i i . roln : c, fourth ventricle, and, 



florin, which traverses a Behind it, valve of Vieusseiis; d, 



iter, and, behind it, corpora quad- 

 rigemina ; e, pineal body ; /, optic 

 thalamus looking into the third 

 ventricle, and, in front of it, an 

 open passage from the third to 

 the lateral ventricle, called fora- 

 men of Monro ; g, left layer of 

 septum lucidum bounding the fifth 

 ventricle, and, beneath it, the 

 foriiix ; h, posterior extremity of 

 corpus callosum above the trans- 

 verse fissure ; i, optic nerve ; Jc, 

 pituitary body ; I, one of the cor- 

 pora albicantia. 



The cerebral hemispheres ill man form by far the most 

 bulky part of the brain. They are covered with a thick 

 coating of grey matter of stratified structure, exhibiting an 

 arrangement of corpuscles and fibres connecting one part of 

 it with another, and the whole with the parts of the brain 

 from which the hemispheres arise, as illustrated in fig. 101. 

 This grey master is thrown into a number of convolutions 

 arranged on a definite plan, though varying in their finer 



space left between the free 

 edge of the tentorium and 

 the body of the sphenoid 

 bone. This isthmus, as 

 seen from below, consists 

 of two thick pillars, the 

 crura cerebri, emerging 

 above the poiis "Varolii, 

 diverging as they ascend, 

 and almost immediately 

 concealed by the two cere- 

 bral hemispheres. 



