734 



THE POPULAR SCIENCE MONTHLY. 



rectly above the medulla is what is known as the pons Varolii. There 

 are masses of cell-matter scattered at irregular intervals through the 

 pons, but it is made up principally of longitudinal and transverse fibers. 

 The longitudinal fibers connect the medulla with the cerebrum, 

 while the transverse fibers unite the halves of the cerebellum. This 

 organ, the cerebellum, is made up of two hemispheres or lateral lobes 

 and a median or central lobe. The cell-matter lies on the outside, the 



fibers are within. The external 

 surface of the organ has a foliated 

 appearance, caused by its subdivis- 

 ions into multitudes of thin plates 

 by numerous fissures. This sub- 

 division allows great increase of 

 cell-matter by numerous fine con- 

 volutions, and the matter is further 

 augmented through penetration 

 within of arborescent processes of 

 cell-substance. 



The next portion of nerve-mat- 

 ter to be noticed is the cerebrum. 

 This makes up more than four 

 fifths of the contents of the en- 

 cephalon. The cerebrum is egg- 

 shaped, but flattened on its under 

 side, and lies in the cranium with 

 its small end forward. It is di- 

 vided into halves or hemispheres 

 by a great longitudinal fissure. 

 These halves, however, are con- 

 nected by a middle portion of 



Fig. 2. — Motor Nerve -Cells connected by 

 intercellular processes (6, 6), and giving 

 orijrin to outgoing fibers (c, c, c, and a). 4. 

 Multipolar cell containing much pigment 

 around nucleus. Diagrammatic. (Vogt.) 



nerve-substance called the corpus callosum. The surface of the cere- 

 brum is molded into numerous convolutions marked off from one 

 another by furrows. The cell-matter of the cerebrum is external, it 

 follows the convolutions, and is from one twelfth to one eighth of an 

 inch in thickness. 



The hemispheres of the cerebrum have been divided into lobes 

 called the frontal, parietal, occipital, and temporo-sphenoidal lobes. 

 These divisions are in part arbitrary, while in part they rest upon cer- 

 tain primary fissures, such as the fissure of Sylvius and the fissure of 

 Rolando. It should be borne in mind that these different regions of 

 the cerebrum are not distinct departments physiologically independent. 

 The convolutions are exteriorly connected among themselves and also 

 with convolutions of neighboring lobes. They have, besides, interior 

 connections through bundles of fibers which pass from one convolution 

 to the base of an adjacent convolution. If we remove the encephalic 

 mass and look at it from beneath, we see the medulla as a continua- 



