THE NERVOUS SYSTEM 



167 



E. THE CRURA CEREBRI AND CORPORA 

 QUADRIGEMINA. 



Above the pons Varolii, the two halves of the medulla 

 diverge from one another and form the peduncles of the 

 cerebrum (Fig. 90, CC., P.), while posteriorly the two superior 

 peduncles of the cerebellum having crossed join together 

 (8.C.P.). Above these, two swellings develop on each side 

 the anterior and posterior corpora quadrigemina (Fig. 82, 

 p. 154). 



The crusta, or anterior parts of each peduncle of the 



FIG. 90. Cross Section through Anterior Corpora Quadrigemina and Cerebral 

 Peduncles, A.S., Aqueduct of Sylvius; III., Nucleus of Third Nerve; 

 S.C.P., Superior Cerebellar Peduncles; F., Fillet; P., Pyramidal Tract; 

 CC., Cerebello-cerebral Fibres. (After BRUCE.) 



cerebrum, is composed, in its central part, of the pyramidal 

 fibres passing down from the cerebrum to the spinal cord 

 (P.), and, on each side, of the cerebello-cerebral fibres pass- 

 ing upwards from the pons (CC.). The posterior part, or 

 tegmentum, contains 1st, the fillet fibres going partly to 

 the corpora quadrigemina, partly onwards to the thalamus 

 opticus (P.); 2nd, the nuclei of the 3rd and 4th cranial 

 nerves; 3rd, the fibres of the superior peduncles of the 

 cerebellum which cross the middle line (S.C.P.); and 4th, 

 the red nuclei in which most of these fibres end. 



