210 



DISSECTION OF THE BRAIN. 



resting on its under surface, let the knife be carried vertically through tlie 

 centre of tin 1 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 interpositum ; 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, b. 



a. Corpus striatum. 



b. Optic thalamus. 



(?. Anterior commissure. 

 d. Middle or soft commissure. 

 . Posterior commissure. 

 y. Pineal body. 



/. Peduncle of the pineal b <>dy. 

 h and i. Left pair of the corpora quadrigeruina. 

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

 medulla oblangata. 



k. Valve of Vieussens. 

 I. Upper peduncle of the cerebellum, 

 o. Erninentia teres. 

 p. Anterior fossa. 

 r. Posterior fossa. 

 ft. Posterior pyramid. 



4. Origin of the fourth nerve from the valve of 

 Vieusseus. 



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 



