534 THE BRAIN 



Lobus Pyramidis. The pyramid is connected with the bi ventral 

 lobule on each side by a faint ridge which crosses the sulcus vallecukv. 

 The term lobus pyramidis is given to the three lobules which are thus 

 associated with each other. 



Lobus Tuberis. The tuber vermis , which forms the most posterior part 

 of the vermis, is composed of several folia, which run directly into the 

 inferior semilunar lobule on each side. The three parts of the lobus tuberis 

 are thus linked together. The inferior semilunar lobule is traversed by 

 two, or it may be three, curved fissures. The most anterior of these cuts 

 off a narrow, curved strip of cerebellar surface called the lobuhis gracilis. 



Dissection.- A median section should now be made through the vermis 

 of the cerebellum and the two medullary vela into the cavity of the fourth 

 ventricle. When the two parts of the cerebellum are drawn slightly 

 asunder, a view of the fourth ventricle is obtained ; further, the connections 

 of the two medullary vela and the arrangement of the peduncles of the 

 cerebellum can be more clearly understood. 



Arbor Vitse Cerebelli. The cut surface of the cerebellum 

 presents a very characteristic appearance. The grey matter 

 on the surface stands out distinctly from the white matter in 

 the interior. Further, the complete manner in which the 

 surface is cut up by the sulci into secondary and tertiary folia 

 is seen. The central mass of white matter in the vermis is 

 termed the corpus medullare. From this, prolongations pass 

 into the various lobules, and these give off branches to supply 

 each folium with a central white stem or core. The term 

 arbor vitcz is applied to the appearance which consequently 

 results when a section is made through the cerebellum. 



Cerebellar Peduncles. The cerebellar peduncles are the 

 structures which connect the cerebellum with 'the medulla 

 oblongata, the pons and the mid-brain. They are three in 

 number on each side viz., the middle, the superior, and 

 the inferior. They are all directly connected with the white 

 medullary centre of the cerebellum, and are composed ot 

 fibres which emerge from or enter the white central sub- 

 stance of the organ. 



The middle peduncle is the brachium pontis, and is much 

 the largest of the three. It is formed by the transverse 

 fibres of the pons, and it enters the cerebellar hemisphere on 

 the lateral side of the other two. The lips of the anterior 

 part of the great horizontal sulcus are separated widely from 

 each other to give it admission. 



The inferior peduncle is simply the restiform body of the 

 medulla oblongata. Leaving the dorsum of the medulla 

 oblongata it turns sharply posteriorly and enters the cerebellum 

 between the other two peduncles. 



