BASE OF THE BRAIN. 519 



The anterior perforated space is situated at the inner side of the fissure of 

 Sylvius. It is of a triangular shape, bounded in front by the convolution of the 

 anterior lobe and roots of the olfactory nerve ; behind, by the optic tract ; externally, 

 by the middle lobe and commencement of the fissure of Sylvius ; internally, it is 

 continuous with the lamina cinerea, and crossed by the peduncle of the corpus 

 callosum. It is of a grayish color, and corresponds to the under surface of the 

 corpus striatum, a large mass of gray matter, situated in the interior of the brain; 

 it has received its name from being perforated by numerous minute apertures for 

 the transmission of small straight vessels into the substance of the corpus striatum. 



The optic commissure is situated in the middle line, immediately behind the 

 lamina cinerea. It is the point of junction between the two optic nerves. 



Immediately behind the diverging optic tracts, and between them and the 

 peduncles of the cerebrum (crura cerebri} is a lozenge-shaped interval, the inter- 

 peduncular space, in which are found the following parts, arranged in the following 

 order from before backwards : the tuber cinereum, infundibulum, pituitary body, 

 corpora albicantia, and the posterior perforated space. 



The tuber cinereum is an eminence of gray substance, situated between the 

 optic tracts and the corpora albicantia ; it is connected with the surrounding parts 

 of the cerebrum, forms part of the floor of the third ventricle, and is continuous 

 with the gray substance in that cavity. From the middle of its under surface, 

 a conical tubular process of gray matter, about two lines in length, is continued 

 downwards and forwards to be attached to the posterior lobe of the pituitary body ; 

 this is the infundibulum. Its canal, funnel-shaped in form, communicates with 

 the third ventricle. !Jt 



The pituitary body is a small, reddish-gray, vascular mass, weighing from five 

 to ten grains, and of an oval form, situated in the sella Turcica, in connection with 

 which it is retained by the dura mater which forms the inner wall of the cavernous 

 sinus. It is very vascular, and consists of two lobes, separated from one another 

 by a fibrous lamina. Of these, the anterior is the larger, of an oblong form, and 

 somewhat concave behind, where it receives the posterior lobe, which is round. 

 The anterior lobe consists externally of firm yellowish-gray substance, and inter- 

 nally of a soft pulpy substance of a yellowish-white color. The posterior lobe is 

 darker than the anterior. In the foetus it is larger proportionally than in the 

 adult, and contains a cavity which communicates through the infundibulum with 

 the third ventricle. In the adult it is firmer and more solid, and seldom "contains 

 any cavity. Its structure, especially the anterior lobe, is similar to that of the 

 ductless glands. 



The corpora albicantia are two small round white masses, each about the size of 

 a pea, placed side by side immediately behind the tuber cinereum. They are formed 

 by the anterior crura of the fornix, hence called the bulbs of the fornix, which, 

 after descending to the base of the brain, are folded upon themselves, before passing 

 upwards to the thalami optici. They are composed externally of white substance, 

 and internally of gray matter ; the gray matter of the two being connected by a 

 transverse commissure of the same material. At an early period of foetal life 

 they are blended together into one large mass, but become separated about the 

 seventh month'. 



The posterior perforated space or pons Tarini corresponds to a whitish-gray 

 substance, placed between the corpora albicantia in front, the pons Varolii behind, 

 and the crura cerebri on either side. It forms the back part of the floor of the 

 third ventricle, and is perforated by numerous small orifices for the passage of 

 bloodvessels to the thalami optici. 



The crura cerebri or peduncles of the cerebrum are two thick cylindrical bundles 

 of white matter, which emerge from the anterior border of the pons, and diverge 

 as they pass forwards and outwards to enter the under part of either hemisphere. 

 Each crus is about three-quarters of an inch in length, and somewhat broader in 

 front than behind. They are marked upon their surface with longitudinal stria?, 

 and each is crossed, just before entering the hemisphere, by a flattened white band. 



