290 



COORDINATION AND SENSATION 



it with the hindbrain. On account of the great size of the 

 cerebrum, the midbrain is entirely concealed from view 

 when the other parts occupy their normal positions. How- 

 ever, if the cerebrum is pulled away from the hindbrain, 

 it is brought into view somewhat as in Fig. 1 30. 



The midbrain carries upon its back and upper surface four small 

 rounded masses of cell-bodies, called the corpora quadrigemina. The 

 upper two of these bodies are connected with the eyes ; the lower two 

 appear to have some connection with the organs of hearing. On the 

 front and under surface, the midbrain separates slightly as if to form 

 two pillars, which are called the crura cerebri, or cerebral peduncles. 

 These contain the great bundles of nerve fibers that connect the cere- 

 brum with the parts of the nervous system below. 



The Hindbrain lies beneath the back portion of the 

 cerebrum, and occupies the enlargement at the base of the 

 skull. It forms about one eighth of the entire brain, and 

 is composed of three parts the cerebellum, the pons, 

 and the bulb. 



The Cerebellum is a flat and somewhat triangular struc- 

 ture with its upper surface fitting into the triangular under 

 surface of the back of the cerebrum. . It is divided into 

 three lobes a central lobe and two lateral lobes and 

 weighs about two and one half ounces. In its general 

 form and appearance, as well as in the arrangement of its 

 cell-bodies and axons, the cerebellum resembles the cere- 

 brum. It differs from the cerebrum, however, in being 

 more compact, and in having its surface covered with nar- 

 row, transverse ridges instead of the irregular and broader 

 convolutions (Fig. 132). 



The Pons, or pons Varolii, named from its supposed re- 

 semblance to a bridge, is situated in front of the cerebel- 

 lum, and is readily recognized as a circular expansion which 

 extends forward from that body. It consists largely of 



