136 



LECTURES ON THE CENTRAL NERVOUS SYSTEM. 



In the hemispheres the white substance is rather plentiful ; 

 but in the vermis it is scanty. The accompanying- sagittal section 

 (Fig. 81) through the cerebellum passes directly through the 

 vermis. It shows the white substance of the latter prolonged 

 anteriorly into a thin membrane, the velum medullary anticum, 

 which extends toward the corpora quadrigemina. This thin 

 membrane, spread out between the anterior peduncles of the 

 cerebellum, marks the point where the roof of the mid-brain is 

 continuous with the roof of the hind-brain. Upon it lies the 

 most anterior lobule of the cerebellum, the lingula. 



The peculiar appearance presented by a sagittal section of 



FIG. 81. 

 Sagittal section through the middle of the vermis. 



Vert. A., Vertical branch. Boriz. A., Horizontal branch. 



the vermis gave rise to its ancient name, the arbor vitse. The 

 central mass of white matter is called the corpus trapczoides. 

 The lingula, lobus centralis, uvula, and nodulus all communicate 

 separately with it. A number of the lobes of the monticulus 

 have a common connection with the corpus trapezoides, and 

 form the vertical branch of the arbor vitoe. The posterior portion 

 of the monticulus, the folium cacuminis, and the tuber valvulae 

 that is to say, the lobes situated at the posterior edg-e of the 

 cerebellum form the horizontal branch of the arbor vitse. 



Posteriorly, the velum medullare posticum passes out from 

 the cerebellum, forms the roof of the fossa rhomboidalis, and is 



