788 



THE NERVOUS SYSTEM 



in most of the mammalia the vermis is the largest and most evident of the parts, 

 and it is practically the only part which exists in the fishes, reptiles, and birds. In 

 man, owing to the fact that the vermis does not keep pace in development with the 

 hemispheres, there results a very decided notch between the two hemispheres along 

 the line of the entire ventral and inferior aspect of the cerebellum, the floor of this 

 notch being the surface of the vermis. The inferior portion of the notch is the 

 posterior cerebellar notch (incisura marsupialis) ; its prolongation above is wider 

 than below, and is termed the superior cerebellar notch. It is occupied by a fold 

 of the dura mater, the falx cerebelli. With the variations in contour of the cere- 

 bellum, certain of its sulci are broader and deeper, and merit the name fissures. 

 These are more or less definitely placed, and subdivide the hemispheres into lobes 

 and the vermis (the median lobe) into lobules. 



Dorsal surface. The dorsal surface is bounded from the inferior and ventral 

 surface by the horizontal fissure, coursing along the inferior borders of the cerebel- 

 lar hemispheres. Between this and the extreme anterior border are two other fis- 

 sures, the posterior and anterior semilunar fissures. These, like the horizontal 



FIG. 584. SECTION OF HEAD PASSING THROUGH THE MASTOID PROCESSES OP THE TEMPORAL 

 BONES AND BEHIND THE MEDULLA OBLONGATA. SHOWING THE POSITION OF THE CERE- 

 BELLUM. 

 (From a mounted specimen in the Anatomical Department of Trinity College, Dublin.) 



Superior sagittal 

 sinus 



CORPUS 

 CALLOSUM 



Cltorioid plexus 

 Veins of Galen 



Transverse sinus 



falx cerebri 



f'A I'D A TE 

 NUCLEUS 



f- LA TF.RA 7, 



VKSTRICLE 



... i Superior petrosal 



~~^ ' MASTOID ANTRUM 



Transverse sinus 

 MASTOID PROCESS 



fissure, may be traced, with slight interruptions, across the mid-line, and conse- 

 quently mark off not only the two hemispheres but also the vermis into correspond- 

 ing divisions. 



The superior semilunar lobe (postero-superior lobe) of each hemisphere lies 

 between the horizontal and the posterior semilunar fissures. It largely composes the 

 inferior border of the cerebellum, and, therefore, is the longest of the lobes. 



The remaining dorsal surface of the hemispheres, because of the frequently less 

 complete development of the anterior semilunar fissure, is sometimes referred to as 

 the quadrangular lobe, with its posterior and its anterior portions. On the other 

 hand, especially when the anterior semilunar fissure is well marked, this area may 

 be divided into (1) the posterior semilunar lobe, between the posterior and anterior 

 semilunar fissures, and (2) the anterior semilunar lobe, anterior to the anterior semi- 

 lunar fissure. 



The dorsal aspect of the vermis, the superior vermis, because of the fusion of 

 the hemispheres, is, for the most part, a slight ridge, the monticulus, instead of 

 a depression. However, in the inferior portion of the dorsal surface the depression 



