ANATOMY AND PHYSIOLOGY OF THE BRAIN. 413 



convolutions to appear in the lowest animals possessed of a 

 cerebrum. 



On turning to the base of the brain, a number of objects 

 come into view, the principle of which we will enumerate, 

 commencing from behind. From the anterior border of the 

 pons Varolii start out two considerable columns, the pillars 

 of the brain, or crura cerebri (d d.) These diverge in pass- 

 ing forward towards the right and left hemispheres, and 

 leave between them a space known as the intrapeduncular 

 space. The cerebral pillars are crossed in a direction from 

 without forward, and inward by two rounded white bundles 

 (optic tracts), (2" 2"), which, on reaching the median line 

 suffer an interchange of fibres with each other, so as to form 

 the optic commissure (2'.) The optic tracts form the ante- 

 rior boundary of the intrapeduncular space. In the intra- 

 peduncular space is the pituitary body (e), the use of which 

 is unknown. Beneath this is a mass of grey matter, perfo- 

 rated by a canal which leads to the third ventricle (infun- 

 dibulum), close beside the last is a small grey mass (tuber 

 cinerium), behind which is a white body (corpus albicans), 

 and still more posteriorly the posterior perforated space, 

 through which many fibres from the medulla pass upward 

 to gain the cerebral hemispheres. 



In front of the optic tracts are the anterior perforated 

 spaces which lie beneath two striated bodies (corpora 

 striata) placed on the floor of the lateral ventricles. In 

 front of each anterior perforated space is the olfactory bulb, 

 a considerable prolongation of nervous matter, grey with- 

 out, white within, and containing a cavity which communi- 

 cates with that of the corresponding lateral ventricle. 



Turning once more to the superior aspect of the brain, and 

 separating the hemispheres, we meet at the bottom of the 

 longitudinal fissure with a mass of white matter (corpus 



