86 ANATOMY FOE, NURSES. [CHAP. VII. 



the floor of a cavity between the two halves or hemispheres of 

 the cerebellum. The cavity, called the fourth ventricle, is 

 an expanded continuation of a tiny central canal which runs 

 throughout the whole length of the spinal cord. 



The cerebellum, or little brain, overhangs the fourth ventricle. 

 It is of a flattened oblong shape, and measures from three and a 

 half inches to four inches (89 to 102 mm.) transversely, and 

 from two to two and a half inches (51 to 63 mm.) from before 

 backwards. It is divided in the middle line into two halves 



SJ 



FIG. 73. THE BASE OF THE BRAIN. 1, longitudinal fissure; 2, 2, anterior lobes 

 of cerebrum; 3, olfactory bulb; 7, optic commissure; 9, 3d nerve; 11, 4th nerve; 

 13, 5th nerve ; 14, crura cerebri ; 15, 6th nerve ; 16, pons Varolii ; 17, 7th nerve ; 19, 

 8th nerve; 20, medulla oblongata; 21, 9th nerve; 23, 10th nerve; 25, llth nerve; 

 27, 12th nerve ; 28, 29, 30, 31, 32, cerebellum. 



or hemispheres by a central depression, each half being sub- 

 divided by fissures into smaller portions or lobes. The surface 

 of the cerebellum is traversed by numerous curves or furrows, 

 which vary in depth. In the medulla oblongata, the gray 

 matter is placed in the interior, and the white on the exterior ; 

 in the cerebellum, the gray is on the outside, and the white 

 within. 



The pons Varolii, or bridge of Varolius, lies in front of the 

 medulla oblongata. It consists of alternate layers of transverse 



