782 



THE CENTRAL AXIS OF THE NERVOUS SYSTEM. 



layer (substantia ferrugineu) — has a yellow tint, and a mass of nuclei pressed 

 against one another. 



If the direction of the white substance fibres is traced, 

 Fig- ■*3i- it will be found that some form an intra-cerebellar com- 



missural system, while others constitute a radiation system 

 fy-i/r'i^^ that unite the cerebellum to the other parts of the brain. 



The first extend from one corpus rhomboideum to the other, 

 across the cerebellum, or in following the middle cerebellar 

 peduncles. The second represent the anterior and posterior 

 cerebellar peduncles and a part of the middle peduncle. 

 The anterior peduncles, after intercrossing, pass into the 

 thalami optici (red nmlei of Stilling) ; the posterior enter 

 the nuclei of the restiform bodies and ohvary body, where 

 they become united to the sensory system of the spinal 

 cord ; lastly, the middle ones, after intercrossing, disappear 

 in the grey nuclei of the pons Varolii. 



The prolongations of the large cells in the cortex cere- 

 belli — also named the cells of Purkinje — are continuous with 

 the fibres of the white substance. 



SECTION OF THE COR- 

 TICAL SUBSTANCE OF 

 THE CEREBELLUM. 



a,Medullary substance, 

 showing its fibres; 

 6, substantia ferru- 

 ginea, composed of 

 fibres and cell-nu- 

 clei ; c, grey surface, 

 granular at the sur- 

 face, and contain- 

 ing large multipolar 

 branching cells near 

 the substantia fer- 

 ruginea. 



Differential Characters in the Cerebellum of other than 

 SoLiPED Animals. 



The external and internal conformation of the cerebellum offers 

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

 volume, compared with that of the other encephalic lobes, is not in- 

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

 bellum and that of the brain of the Horse is as 1 to 7 ; in the Ox it is 

 as 1 to 9 ; the Dog 1 to 8 ; the Cat 1 to 6 ; and the Sheep 1 to 3. The 

 cerebellar cortical convolutions are less numerous than in the Horse. 

 Leuret has found 175 lamellae in the middle cerebellar lobe of the 

 Ox, 77 in the Sheep, 66 in the Cat, and 32 in the Rabbit. These 

 are the only differences to be noted. 



Comparison of the Cerebellum op Man with that of Animals. 



In Man, the encephalic mass being enormous, the cerebellum is 

 absolutely more considerable in volume than in the larger domesticated 

 animals ; though, in proportion to the cerebral hemispheres, it is 

 smaller than in the Ox, its relation to the latter lobes being as 1 to 8. 



It is covered by the occipital lobes of the brain ; 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 and concealed beneath the lateral lobes, which are so large tiiat they have 

 been named the cerebellar hemispheres. The fissure which separates these hemispheres is 

 named the great middle fismre of the cerebellum ; it lodges the falx cerebelli. The inferior 

 vermis forms a free projection in which is the fourtli ventricle ; this is termed the uvula of the 

 cerebellum. The uvula is connected at each side with the valves of Tan/w'— laminae of nerve- 

 substance lodged for the most part in the fourth ventricle, and hidden by the lower face of the 

 cerebellar hemispheres. Tlie 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 tonsil, the second the pneumogastric lobule (oi flocculus). 



Article IV. — The Cerebrum. 

 The cerebrum, the principal portion of the brain, comprises the two anterior 



