THE FORE-BRAIN. 289 



It is chiefly formed of two large convoluted masses, sepa^ 

 rated from one another by a deep fissure, and known as 

 the cerebral hemispheres. The great size of these is very 

 characteristic of the human brain. Beneath each cere- 

 bral hemisphere is an olfactory lobe (/, Fig. 84), incon- 

 spicuous in man but often larger than the cerebral hemi- 

 spheres, as in most fishes. The mid brain, #, forms a 

 connecting isthmus between the two other divisions. The 

 hind-brain consists of three main parts: on its dorsal side 

 is the cerebellum, B, Fig. 82; on the under side is the 

 pons Varolii, C, Fig. 82; and behind is the medulla ob- 

 longata, D, Fig. 82, which joins the spinal cord. 



In nature the main divisions of the brain are not sepa- 



Cbl 



FIG. 83. The brain from the left side. C6, the cerebral hemispheres forming 

 the main bulk of the fore-brain; Cbl, the cerebellum; Mo, the medulla oblon- 

 gata; P, the pons Varolii; *, the fissure of Sylvius. 



By what is the fore-brain chiefly formed? What lies below the 

 cerebral hemispheres? Are the olfactory lobes ever larger than the 

 cerebral hemispheres? What does the mid-brain form? Name the 

 main divisions of the hind-brain? State their relative positions. 

 What part of the brain joins the spinal cord? 



