CRUKA CEREBRI AND CORPORA QUADRIGEMINA 179 



becomes difficult. This may be readily demonstrated by 

 setting a poker vertically on the floor, holding it in the 

 hand, placing the forehead on the top, walking rapidly 

 three times round it, then standing up and trying to walk 

 out of the room. The sudden stoppage of the rotatory 

 movement causes a disturbance in the semicircular canals 

 giving a sense of rotation in the opposite direction, while 

 the eyes show that no rotation is taking place. The feeling 

 of giddiness is, however, not the cause of the loss of balanc- 

 ing, but a mere accompaniment. (Practical Physiology.} 



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. Cross Section through Anterior Corpora Quadrigemina and Cerebral 

 Peduncles. A.S., aqueduct of Sylvius; ///., nucleus of third nerve; 

 S.C.P., superior cerebellar peduncles; F., mesial fillet; f\, lateral 

 fillet ; P., pyramidal tract ; CO., cerebello-cerebral fibres (Human). 

 (After BRUCE.) 



(fig. 90, CO., P.), while posteriorly the two superior peduncles 

 of the cerebellum come together (S.C.P.}. Above these, two 

 swellings develop on each side the anterior and posterior 

 corpora quadrigemina (fig. 83, p. 168). 



