164 THE HUMAN BODY. 



hemispherical eminences, the corpora quadrigemina. On 

 its ventral side it exhibits two semicylindrical pillars (seen 

 under the nerve /Fin Fig. 70*), known as the crura cere- 

 bri. The hind-brain consists of three main parts: on its 

 dorsal side is the cerebellum, B, Fig. 66, consisting of a 

 right, a left, and a median lobe ; on the ventral side is the 

 \)o ns Varolii, C, Fig. 66, and behind the medulla oNongata, 

 D, Fig. 66, which is continuous with the spinal cord. 



In nature the main divisions of the brain are not sepa- 

 rated so much as has been represented in the diagram for 



FTG. 67. The brain from the left side. Cb, the cerebral hemispheres forming 

 the main bulk of the fore-brain ; Cbl, the cerebellum ; Mo, the medulla oblon- 

 gata ; P, the pons Varolii ; *, the fissure of Sylvius. 



the sake of clearness, but lie close together as represented 

 in Fig. 67, only some folds of the membranes extending 

 between them; and the mid-brain is entirely covered in on 

 its dorsal aspect. Nearly everywhere the surface of the 

 brain is folded, the folds, known as gyri or convolutions, 

 being deeper and more numerous in the brain of man than 

 in that of the animals nearest allied to him; and in the human 

 species more marked in the higher than in the lower races. 

 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 



* P. 169. 



