ANATOMY OF THE NERVOUS SYSTEM 



125 



the two other divisions and presents on its dorsal side four hemi- 

 spherical eminences, the corpora quadrigemina or colliculi. On 

 its ventral side it exhibits two semicylindrical pillars (seen under 

 the nerve IV in Fig. 64), known as the crura cerebri. The hind- 

 brain consists of three main parts: on its dorsal side is the cere- 

 bellum, B (Fig. 60), consisting of a right, a left, and a median lobe; 

 on the ventral side is the pons Varolii, C (Fig. 60), and behind 

 that the medulla oblongata, D (Fig. 60), which is continuous with 

 the spinal cord. 



In nature, the main divisions of the brain are not separated so 

 much as has been represented in the diagram for the sake of clear- 

 ness, but lie close together, as represented in Fig. 61, only some 



Cc. 



Po. 



C.q. 



Th. 



'Sp.c. Mo. P. o.c. p.t. 



FIG. 62 Diagram of the left half of a vertical median section of the brain. (Sobotta- 

 McMurrich, Atlas and Text-book of Human Anatomy). H, H, convoluted inner surface of 

 left cerebral hemisphere; Cc, corpus callosum; Th, optic thalamus; e.g., corpora quad- 

 rigemina; Cb, cerebellum; Sp. c, spinal cord; Mo, medulla oblongata; P, pons Varolii; 

 oc, oculo-motor nerve; pt, pituitary body; op, optic nerve; Ro, fissure of Rolando; Po, 

 parieto-occipital fissure; Fr, frontal lobe; Pa, parietal lobe; O, occipital lobe. 



folds of the membranes extending between them; and the mid- 

 brain is entirely covered in on its dorsal aspect. Nearly every- 

 where 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 



