530 THE BRAIN 



the culmen, and a posterior sloping ridge, the declive. Posterior 

 to the declive, in the anterior boundary of the posterior notch, 

 lies a single folium called the folium vermis. 



On the inferior surface of the cerebellum, the distinction 

 between the three constituent parts of the organ is much 

 better marked. On that aspect the hemispheres are full, 

 prominent and convex, and they are separated by a deep, 

 median hollow which is continued forwards from the posterior 

 notch. This hollow is termed the vallecula cerebelli, and in its an- 

 terior part the medulla oblongata is lodged. If the medulla is 

 forced away from the cerebellum, and the lateral hemispheres 

 are pulled apart so as to expose the upper boundary of the 

 vallecula, it will be seen that this is formed by the inferior 

 surface of the vermis, and, further, that the vermis is separated, 

 on each side, from the corresponding lateral hemisphere by a 

 distinct furrow, termed the sulcus vallecula. 1 



If the margin of the vermis, where it forms the posterior 

 boundary of the anterior notch on the superior aspect of 

 the cerebellum, is gently raised, and at the same time the 

 mesencephalon is pulled anteriorly, two strands lying upon 

 the dorsal aspect of the pons will be seen. These are 

 the brachia conjunctiva cerebelli (O.T. superior peduncles]. 

 They emerge from the white matter of the cerebellum, 

 converge as they proceed upwards, and, finally, they dis- 

 appear under the inferior quadrigeminal bodies. The thin 

 lamina which is stretched across between them is the anterior 

 medullary velum. It" is continuous below with the white core 

 of the vermis, and it helps to form the roof of the upper 

 part of the fourth ventricle. From its dorsal surface, close 

 to the inferior quadrigeminal body, the small trochlear nerves 

 emerge. 



Certain of the sulci which traverse the surface of the 

 cerebellum, deeper and longer than the others, map out 

 districts which are termed lobes. The most conspicuous of 

 all these clefts is the great horizontal sulcus. 



Great Horizontal Sulcus of the Cerebellum. The great 

 horizontal sulcus begins anteriorly, and passes round the 

 circumference of the cerebellum, cutting deeply into its lateral 

 and posterior margins. Anteriorly, its lips diverge from each 



1 As this is done the epithelial roof of the fourth ventricle and its covering 

 of pia mater will be torn away, and the lower part of the floor or anterior 

 boundary of the fourth ventricle will be displayed. 



