12 BEAN. 



3. Gently separate the two hemispheres, cutting through the strands of 

 arachnoid which prevent this, until you come to a white band. 

 (a) The corpus callosum. 



(&) Note running along the median line of this the vein of the 

 corpus callosum. 

 B. On the basal surface of the brain note: 



I. In the medulla: 



1. The anterior median fissure: 



2. On each side of this a longitudinal band, the pyramid. 



3. Lateral to this a narrow, curved band and ventrally a small, oval 



eminence, the olive. 



4. The restiform body, external. 



II. In the midbrain region : 



1. A narrow, transverse band of fibers over which the pyramids run, 



trapezoid body. (This is covered by the pons in the human brain). 



2. A broad, transverse band, the pons. 



III. In the midbrain region : 



1. Passing forward and ovitward from the pons, the peduncles of the 



cerebrum. 



2. The triangular space between, posterior perforated substance. 



3. Forming the anterior boundary of the posterior perforated substance — 



a rounded, whitish body indistinctly divided by a longitudinal fissure 

 into 2, the mammillary bodies. 



4. In front of these a slit, the infundibulum. 



IV. In the forebrain region: 



1. Temporal lobes. 



2. The lateral fissure (Sylvius), separating them from the remainder of 



the brain. 



3. The lower end of the longitudinal fissure. 



4. Anteriorly, the olfactory bulb. 



5. Leading back from these, the olfactory tracts. 



(a) Passing out and back to the summit of the temporal lobes, the 



outer olfactory tracts. 

 (6) Passing back and inward and soon lost from view by turning 



into the longitudinal fissure, the inner olfactory tract. 



6. Passing transversely from the. tip of the temporal lobes to the longi- 



dinal fissure and lying underneath the optic commissure is the so- 

 called crus of the corpus callosum. 



7. Between the two olfactory tracts and 6 is the anterior perforated 



substance on each side. The anterior part of each space is called 

 the olfactory trigone in vi'hich a third or median olfactory tract can 

 be seen to have its termination. 



Make a median, longitudinal (sagittal) section of the brain. 



I. Note the arrangement of the white and the gray matter in the median section 



of the cerebellum. 



II. Note the anterior velum forming the roof of the anterior part of the IV 



ventricle and lying below the cerebellum. 



III. Note the depression on the under surface of the cerebrum where the superior 



(anterior) velum is attached and where the inferior (posterior) velum 

 starts. 



