BASE OF THE BRAIX 589 



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

 following order from before backwards: the tuber cinereum, infundibulura, 

 pituitary body, corpora albicantia, and the posterior perforated space. 



The tuber cinereum is an eminence of gray matter, 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, which is funnel-shaped, communi- 

 cates with the third ventricle. 



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 forming 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 internally of a soft pulpy substance of a yellowish-white 

 color. The posterior lobe is darker than the anterior. In the foetus it is larger 

 proportionately than in the adult, and contains a cavity which communicates 

 through the infundibulum with the third ventricle. In fhe 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 them- 

 selves, before passing upwards to the thalami optici. They are composed ex- 

 ternally 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 ( pons Tarini) corresponds to a whitish-gray sub- 

 stance, 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 (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 

 strias, and each is crossed, just before entering the hemisphere, by a flattened 

 white band, the optic tract, which is adherent by its upper border to the peduncle. 

 In the interior of the crura is contained a mass of dark gray matter, called locus 

 niger. The third nerves may be seen emerging from the inner side of either 

 crus; and the fourth nerve winding around its outer side from above. 



Bach crus consists of a superficial and deep layer of longitudinal white fibres, 

 continued upwards from the pons; these layers are separated from each other 

 by the locus niger. 



The superficial longitudinal fibres are continued upwards, from the anterior 

 pyramids to the cerebrum. They consist of coarse fasciculi, which form the 

 free part of the crus, and have received the name of the fasciculated portion 

 of the peduncle, or crust. 



The deep layer of longitudinal fibres are continued upwards, to the cerebrum, 

 from the lateral and posterior columns of the medulla, and from the olivary 



