310 ELEMENTAKY PHYSIOLOGY. [XXX. 



cerebellum, constituting the inferior pedun- 

 cles of the cerebellum. 



4. Turn back the cerebellum, tearing away the pia 

 mater which dips down in front of it. Observe 



a. The corpora quadrigemina, consisting of 

 two round and rather large anterior bodies, 

 and two smaller posterior bodies. The an- 

 terior corpora quadrigemina are partially 

 covered by the cortex of the cerebrum. 



6. The superior peduncles of the cerebel- 

 lum, one on each side, proceeding from 

 the cerebellum as a roundish cord and dis- 

 appearing underneath the posterior corpus 

 quadrigeminum of the same side. 



c. The valve of Vieussens, a thin layer of 

 nervous substance stretching between the 

 superior peduncles, and covering in the an- 

 terior part of the fourth ventricle. In the 

 anterior part of the valve the roots of the 

 fourth nerve may be seen rising from the 

 middle line, and curving round to reach the 

 base of the brain. 



d. Tear away the valve of Vieussens and observe 

 the anterior triangular part of the fourth 

 ventricle, its lateral boundaries are the 

 superior peduncles of the cerebellum. 



5. Note on the under (ventral) surface of the 

 medulla oblongata, without tearing away the 

 pia mater, 



