THE CEREBRUM. 



689 



Fi?. 328 



with the crura cerebelli, and on the other terminate in the cells of the grey 

 substance. 



In the grey spot that forms the corpus rhomboideum, is a great number of 

 large nerve-cells. 



With regard to structure, the grey matter of the cere- 

 bellum may be decomposed into two layers; the super- 

 ficial is very rich in blood-vessels, has a greyish tint, and 

 is composed of large nerve-cells and smaller rounded ele- 

 ments ; the deep layer is of a yellow colour, and also 

 contains nerve-cells and round elements, though the latter 

 are smaller than in the other layer, and have been sometimes 

 mistaken for simple nuclei. 



DTPrEBENTIAL CHARAOTEKS OF THE CEREBELLUM IN OTHER THAN 

 SOLtPED ANIMALS. 



The external and intei nal conformation of the cerebellum offers 

 the closest analogies in the domesticated luammifers. In all, its 

 volume, compared with that of the otiier encephalic lobes, is not 

 invariable. Thus, while the relation between the weight of the cere- 

 bellum and that of the brain of the H(U'se is as 1 to 7 ; with the Ox 

 it is as 1 to 9 ; with the Dog 1 to 8 ; with the Cat 1 to 6 ; and with 

 the Sheep 1 to 3. These are the only differences to be noted 



\m 



fi 



COMPARISON OF THE CEBEBEI.LnM OF MAN WITH THAT OP ANIMALS. 



In Man, the encephalic mass being enormous, the cerebellum 

 is absolutely more considerable in volume than in the larger domesti- 

 cated animals ; though, in pj'oportion to the cerebral hemispheres, it 

 is smaller than in the Ox, its relation to the latter lobes being as 

 1 to 8. 



It is wider than it is long, and projects much beyond the medulla 

 oblongata. It has three lobes; but these are only visible on its 

 lower aspect ; on the opposite face, the median lobe is depressed anil 

 concealed beneatli the lateral lobes, which are so large that they 

 have been named the CKvebellar hemispheres. The inferior veimis 

 forms a free projection in which is the fourth ventricle; this is 

 termed the uvula of the cerebellum. The uvula is connected at each 

 side with the valves of Tarin : laminse of nerve-substance lodged for 

 the most part in tlje fourth ventricle, and hidden by the lower face 

 of the cerebellar hemispheres. The latter constitute, on the sides of 

 the medulla oblongata, two prominences situated one below the other, 

 above the crura cerebelli; the first is designated the amygdala or 

 timsil, the second the pneumogastric lobule (or flocculus). 



CTION OF THE 

 CORTICAL SUB- 

 STANCE OF THE 

 CEREBELLUM. 



Medullary sub- 

 stance, showing 

 its fibres; 6, Sub- 

 stantia ferrugi- 

 nea, composed of 

 fibres and cell- 

 nuclei ; c, Grey 

 surface, granu- 

 lar at the sur- 

 face, and contain- 

 ing large mul- 

 tipolar branch- 

 ing cells near 

 the substantia 

 ferruginea. 



Article IV. — The Ceebbrttm. 



The cerebrum, the principal portion of the encephalon, 

 comprises the two anterior lobes or Jiemispheres of that 

 apparatus : enlargements which are elongated in the direc- 

 tion of the great diameter of the head and cranial cavity, 

 lie beside each other on the middle line, and are united 

 at their central part by a transverse commissure, and by 

 the encephalic isthmus, whose anterior extremity penetrates, inferior ly, 

 into their substance. (See Fig. 329 for a good idea of this penetra- 

 tion.) 



These two lobes together represent an ovoid mass, having its thick 

 extremity adjacent to the cerebellum ; it is depressed from above to below,, 

 deeply divided above, in front, and behind by a median antero-posterior 



