782 



THE CENTRAL AXIS OF THE NERVOUS SYSTEM. 



layer {substantia ferrugined)- 

 asrainst one another. 



-has a yellow tint, and a mass of nuclei pressed 



Fig. 431. 



m 



If the direction of the white substance fibres is traced, 

 it will be found that some form an intra-cerebellar com- 

 missural system, while others constitute a radiation system 

 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 ?iuclei of Stilling) ; the posterior enter 

 the nuclei of the restLorm bodies and olivary 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,Medunary 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 th(! 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 numt-roua 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 iu the Rabbit. These 

 are the only differences to be noted. 



COBIPARISON OF THE CEREBELLUM OF MaN WITH THAT OF AnIMALS. 



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

 absolutely more considerable in volume than in th(^ 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 bniin ; 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 that they have 

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

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

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

 cerehellum. The uvula is connected at each side with the mlves of Tarini — laminae of uerve- 

 snbstiinee lodged for the most part in the fourth ventr.cie, 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 tonsil, the second the pneumogastric lobule (or flocculus). 



Article IV. — The Cerebrum. 

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



