354 NERVOUS SYSTEM; 



SECT. IV.- OF THE CEREBELLUM. 



The Cerebellum, being placed in the posterior fossae of the- 

 cranium, is separated by the tentorium from the posterior 

 lobes of the cerebrum, beneath which it lies. It is connected 

 with the Pons Varolii by a trunk of medullary matter on each 

 side, called the crus of the cerebellum; and which is a root of 

 the medullary matter entering into the composition of the 

 pons. 



It is of a rounded form, and well fitted to the cavity in which 

 it reposes. It is convex above and below; measures about four 

 inches in its transverse diameter, two and a half in thickness, 

 and about the same from before backwards. The upper face 

 is divided into two equal parts or halves, by a middle ridge, 

 while the lower face is divided in the same way by a fossa. 

 These halves are called hemispheres; their surface is marked 

 by many horizontal fissures, the edges of which are kept closed, 

 by the adhesion of the pia mater. 



The fissures are interposed between the laminae or convolu- 

 tions of the cerebellum, which,. for the most part, are concen- 

 tric; the larger fissures are behind, while the shortest are in 

 front, near the annular protuberance. The pia mater pene- 

 trates to the bottom of these fissures, some of which, when ex- 

 posed fully by its removal, are found to extend to the depth of 

 an inch or more. One of these fissures,, which exists on the 

 superior surface of the cerebellum, half an inch distant from 

 the posterior and external margin of the latter, has a circular 

 course, and is so well marked by its size and depth, that it is. 

 called the Sulcus Superior Cerebelli. Another, situated under 

 similar circumstances on the inferior surface of the cerebellum, 

 is called the Sulcus Inferior Cerebelli. On the latter surface,. 

 a;lso, there are two or three more of a middle size, situated 

 Between the sulcus inferior and the annular protuberance. 

 These larger sulci have givem occasion to anatomists to multi- 

 ply most unreasonably the number of lobes of which the cere-, 

 bellum consists. Bichat's mode of description is preferable: 

 he says, that by cutting (vertically) through one of the hemi- 

 spheres of the cerebellum, so as to expose the thickest part of< 



