216 



DISSECTION OF THE BRAIN. 



resting on it> under surface, let the knife be carried vertically through the 

 centre of the vermiform processes; and then the structure of the central 

 uniting part, as well as the boundaries of the fourth ventricle, may be 

 observed on separating the halves of the cerebellum. 



Fig. 68. 



VIEW OF THE THIRD AND FOURTH VENTRICLES. 



The former being obtained by the removal of the velum interpqsitum ; and the latter by dividing 

 vertically the vermiform process of the cerebellum. (From a cast in the Museum of University 

 College.) The third ventricle is the interval in the middle liue between the optic thalami, 6. 



. Corpus striatum. 



b. Optic thalliums. 



c. Anterior commissure. 



d. Middle or soft commissure. 



e. Posterior commissure. 

 ff. Pineal body. 



/. Peduncle of the pineal body. 

 h and i. Left pair of the corpora quadrigemina. 

 The fourth ventricle, ?i, is at the back of the 

 medulla oblangata. 



fc. Valve of Vieussens. 

 I. Upper peduncle of the cerebellum. 

 o. Eminentia teres. 

 p. Anterior fossa. 

 r. Posterior fossa. 

 s. Posterior pyramid. 



4. Origin of the fourth nerve from the valve of 

 Vieussens. 



Structure of the vermiform process (fig. 68). The upper and lower 

 vermiform processes of the cerebellum are united in one central part, which 

 connects together the hemispheres. The structure of this connecting 



