The Fore-Brain


The cerebral hemispheres grow to such a size in man that, with the exception of a few structures on the under surface, they are the only portions of the fore-brain visible on the exterior of the undissected brain. The structures referred to are (a) the olfactory tracts and bulbs, and (b) part of the floor of the third ventricle (the cavity within the back part of the fore-brain). From before backwards the latter presents:

(1) the optic tracts coming downwards and forwards, one on either side; they meet and partially decussate in the middle line, forming the optic commissure or chiasma and from this the two optic nerves (right and left) proceed to the eyeballs;

(2) the tuber cinereum, a small conical swelling from the apex of which extends a short stalk the infundibulum leading down to the pituitary body;

(3) the corpora mamillaria, two little spherical bodies lying side by side;

(4) the posterior perforated spot, a sieve-like area through which numerous small bloodvessels pass (Fig. 29).