574 



THE NERVOUS SYSTEM. 



passes continuously round the circumference of the organ, cutting deeply into it 

 lateral and posterior margins. In front, its lips diverge to enclose the thre 

 cerebellar peduncles as they pass into the interior of the cerebellum. Th 

 horizontal fissure divides the organ into a superior and an inferior part, whic 

 may be studied separately. 



In some cases it meets the corresponding fissure of the other side upon tl 

 vermis, but very often such a confluence does not occur. The folium vermis 

 such cases is not distinguished from the tuber vermis. 



The cerebellum is subdivided somewhat arbitrarily into a median porti< 

 termed the vermis, and two much larger lateral portions, called the hemisphen 

 The demarcation between these main subdivisions of the organ is not ve 

 evident from every point of view. In front, and also behind, there is a mark 

 deficiency or notch. The incisura cerebelli posterior (O.T. marsupial notch) 

 smaller and narrower than the anterior notch. It is bounded at the sides 

 the hemispheres, whilst its bottom is formed by the axial lobe or vermis. 

 is occupied by a fold of dura mater called the falx cerebelli. The incisi 

 cerebelli anterior (O.T. semilunar notch) is wide, and," when viewed from above 

 is seen to be occupied by the inferior quadrigeminal bodies and by the brad 



Pons 



Mesencephalon occup- 

 the incisura anterior ' 



Lobulus culminis 

 Lobtilus 



Central lobule 



Culmen 



Declive 



Folium vermis 



Postero-inferior lobul 



Tuber vermis Incisura posterior 



FIG. 509. SUPERIOR SURFACE OF THE CEREBELLUM. 



conjunctiva. As in the case of the posterior notch, its sides are formed by & 

 hemispheres, and the bottom by the vermis. 



On the superior surface of the cerebellum there is little distinction toe 

 noted between the median lobe and the superior surface of each hemisphere, 

 this aspect the median lobe receives the name of superior vermis, and it fon a 

 high median elevation, from which the surface slopes gradually downwards on J 

 side to the margin of the hemisphere. The superior vermis is highest in f: 

 immediately behind the anterior notch, and from this it shows a somewhat 

 descent towards the posterior notch. This elevation of the superior verm 

 frequently called the monticulus. The folia on the surface of the sup 01 

 vermis are thicker and fewer in number than those on the upper surface of ^ 

 hemisphere. It is this which gives it the worm-like appearance from whic ^ 

 derives its name. 



On the inferior surface of the cerebellum the distinction between the three ] 1 

 constituent parts of the organ is much better marked (Fig. 510). On this a, 1 ^ 

 the hemispheres are full, prominent, and convex, and occupy the cereb 

 fossae in the floor of the cranium. They are separated by a deep median he w 

 which is continued forwards from the posterior notch. This hollow is termec I 

 vallecula cerebelli, and in its anterior part the medulla oblongata is lodged. "V eB 

 the medulla oblongata is raised and the hemispheres are pulled apart, so 

 expose the bottom of the vallecula, it will be seen that this is formed by the v^ 11 



