478 NEUROLOGY. 



the under part of each hemisphere, and terminating in the optic 

 thalami and corpora striata. These cruYa consist of two layers 

 of white matter, with a mass of grey matter, the locus niger, 

 interposed. Both layers are longitudinal, the superficial being 

 continuous with the inferior pyramids, and the deep with the 

 lateral and superior columns of the medulla and olivary fasciculi. 

 They are covered by the corpora quadrigemina and optic thalami, 

 and are crossed in front by the optic tracts and first portion of 

 the optic nerves. These nerves proceed forwards and inwards, 

 and decussate in the median line, the junction being termed the 

 optic commissure. The lozenge-shaped space between the crura 

 and the optic tracts is the interpeduncular space, in which we 

 find the pituitary body or gland {hypophysis cerebri), the 

 infundibulum, the corpus albicans, the locus perforatus posticus, 

 and the pons Tarini. 



The pituitary body or gland, is a small, round, reddish-grey, 

 vascular body, lodged in the sella turcica, where it is held by a 

 fold of dura mater ; it is similar in structure to the ductless, 

 glands, and in the foetus it contains a central cavity, which com- 

 municates, through the infundibulum, with the third ventricle. 



The corpus albicans is a round object, white externally and 

 grey internally, situated behind the optic commissure. It is 

 connected with the crura or bulb of the fornix. From its under 

 surface is prolonged the infundibulum, a conical process of 

 reddish colour, to the summit of which the pituitary body is 

 attached. The funnel-shaped cavity in this process communicates 

 superiorly with the third ventricle of the brain. 



The remaining space between the corpus albicans and the 

 crura of the cerebrum, forming part of the floor of the third 

 ventricle, is the locus perforatum posticus, the numerous minute 

 openings in which are for the passage of blood-vessels to the 

 optic thalami. The white fibres which cross this space from one 

 crus to the other form the pons Tarini. 



On each side, rather to the front of the optic tracts, and ne'^r 

 the commencement of the Sylvian fissure, is a triangular spaco 

 of grey matter, the locus perforatum anticus. This space, like 

 the posterior perforated space, is pierced for the passage of 

 blood-vessels to the corpora striata, which lie immediately above. 



The tuber cinereum, a spherical mass, connected with the 

 corpus striatum, is situated immediately before the optic tract, 

 and behind it is the mammillary eminence. 



