DISSECTION OF THE BRAIN. 77 



B. EXTERNAL CHARACTERS OF THE BRAIN. 



I. The Dorsal Surface of the Brain. 



a. The Cerebral Hemispheres occupy the greater 

 portion of the dorsal surface. They show a number of 

 well-marked fissures and convolutions (sulci and gyri ). 

 The two hemispheres are connected by a broad white 

 commissure, the corpus callosum, which may be seen 

 by gently separating the two hemispheres and tearing 

 or cutting away the pia mater which stretches across 

 from one to the other. The corpus lies well toward 

 the ventral surface of the hemispheres. 



b. The Olfactory Lobes are a pair of large flat 

 tened triangular lobes projecting from the ventral sur- 

 face of the brain, but visible in a dorsal view. 



c. The Corpora Quadrigemina may be exposed 

 by pressing apart the cerebellum and the cerebrum, and 

 tearing away the intervening pia mater. They consist 

 of two pairs of rounded elevations, of which the pos- 

 terior pair are the larger. 



d. The Cerebellum. The whole surface is marked 

 with narrow folds which run both in a transverse and 

 a longitudinal direction. They are seen better if the 

 pia mater is stripped off. The cerebellum is divided 

 into a large median lobe, the vermis, in which the 

 folds run transversely, and two lateral lobes or hemi- 

 spheres in which the folds have a general longitudinal 

 direction. On the outer and under sides of the hemi- 

 spheres the \oo?,e.Jloccular lobes will be seen if the brain 

 has been carefully removed. 



With a pair of forceps tear away carefully the pia 

 mater beneath and posterior to the cerebellum to bring 

 into view the medulla oblongata. 



e. The Medulla Oblongata lies beneath and 



