THE CEREBELLUM. 



493 



experiments, a hemiplegia or hemianaesthesia, following laceration of 

 the brain substance, may disappear within a few days, or even in twenty- 

 four hours, though the mechanical injury be not yet repaired. While 

 therefore we cannot say that either of the cerebral ganglia are the phys- 

 iological organs of sensation or motion, yet their injury, both in animals 

 and in man, generally produces, as its immediate result, hemiplegia or 

 hemiansesthesia, either singly or combined, on the opposite side of the 

 body. 



The Cerebellum. 



The cerebellum, although in man and the quadrupeds much inferior in 

 size to the cerebrum, consists, like it, of a folded layer of gray matter 

 surrounding the mass of white substance which forms its internal por- 

 tion. The cortical layer of gray substance is only about one-half as 

 thick as that of the cerebral hemispheres; being nowhere over 1.5 milli- 

 metre in thickness. But the convolutions of the cerebellum are more 

 compactly arranged than those of the cerebrum, and penetrate into its 

 substance in the form of thin, closely adjacent laminae ; so that it con- 

 tains a comparatively large quantity of gray matter in proportion to its 

 mass. In the white substance of the cerebellum on each side, not far 

 from the median line, there is an isolated deposit of gray matter in the 



i. 163. 



VERTICAL TRANSVERSE SECTION OF THE HUMAN CEREBELLUM AND ME- 

 DULLA OBLONGATA, a little behind the pons Varolii; posterior portion. 1. Medulla 

 oblongata, showing the nucleus of the olivary bodies. 2. Fourth ventricle. 3, 3. White 

 substance of the cerebellum. 4,4. Corpus dentatum of each side. (Henle.) 



form of a thin lamina, folded in irregular, tooth-like convolutions, 

 whence its name of corpus dentatum. This lamina is everywhere closed 

 on its external lateral aspect, but presents an opening at one point 

 toward the median line. It seems to occupy, in the cerebellum, a place 

 analogous to that of the cerebral ganglia above, and to that of the 

 olivary nuclei in the medulla oblongata. 



The gray matter of the cerebellar convolutions is penetrated by fibres 



