530 NERVOUS SYSTEM. 



Some of the diverging fibres end in the cerebral ganglia, whilst others pass 

 through and receive additional fibres from them, and, as they emerge, radiate into 

 the anterior, middle, and posterior lobes of the hemisphere, decussating again with 

 the fibres of the corpus callosum, before passing to the convolutions. 



The transverse commissural fibres connect together the two hemispheres across 

 the middle line. They are formed by the corpus callosurn, and the anterior aud 

 posterior commissures. 



The longitudinal commissural fibres connect together distant parts of the same 

 hemisphere, the fibres being disposed in a longitudinal direction. They form the 

 fornix, the tasnia semicircularis, and peduncles of the pineal gland, the striae 

 longitudinales, the fibres of the gyrus fornicatus, and the fasciculus uncinatus. 



CEREBELLUM. 



The Cerebellum or little brain is that portion of the encephalon which is con- 

 tained in the inferior occipital fossae. It is situated beneath the posterior lobes 

 of the cerebrum, from which it is separated by the tentorium. Its average weight 

 in the male is 5 oz. 4 drs. It attains its maximum weight between the twenty-fifth 

 and fortieth years ; its increase in weight after the fourteenth year being relatively 

 greater in the female than in the male. The proportion between the cerebellum 

 and cerebrum is, in the male, as 1 to 8| ; and, in the female, as 1 to 8|. In the 

 infant, it is proportionally much smaller than in the adult, the relation between 

 them being, according to Chaussier, between 1 to 13 and 1 to 26 ; by Cruveilhier 

 it was found to be 1 to 20. In form, the cerebellum is oblong, flattened from 

 above downwards, its greatest diameter being from side to side. It measures 

 from three and a half to four inches transversely, from two to two and a half 

 inches from before backwards, being about two inches thick in the centre, and 

 about six lines at its circumference, the thinnest part. It consists of gray and 

 white matter : the former, darker than that of the cerebrum, occupies the surface ; 

 the latter, the interior. The surface of the cerebellum is not convoluted like the 

 cerebrum^ but traversed by numerous curved furrows or sulci, which vary in depth 

 at different parts, and correspond to the intervals between the laminae of which its 

 exterior is composed. 



Its upper surface (fig. 270) is somewhat elevated in the median line, and de- 

 Fig. 270. Upper Surface of the Cerebellum. 



pressed towards its circumference; it consists of two lateral hemispheres, connected 

 together by an elevated median portion or lobe, the superior vermiform Drocess. 



