THE BASE OF THE BRAIN 331 



by the union of the two optic tracts. It lies below the lamina 

 cinerea and in front of the tuber cinereum. 



Between the optic tracts and the crura cerebri is a diamond- 

 shaped area, the inter peduncular space. This space includes 

 the tuber cinereum, infundibulum, pituitary body, corpora 

 albicantia, and the posterior perforated space. 



The tuber cinereum is an elevation of gray matter between 

 the optic tracts and corpora albicantia, and forms part of the 

 floor of the third ventricle. From its under surface the infundib- 

 ulum runs down to the pituitary body. The former is hollow 

 and of a conical form, its cavity communicating with the 

 third ventricle. 



The pituitary body, or hypophysis cerebri, is a reddish-gray 

 mass occupying the sella turcica. Its weight is from 4 to 10 

 grains. It consists of two lobes, the anterior and larger of 

 which encloses the posterior. The former is of a yellowish- 

 gray color; the latter in fetal life contains an aperture which 

 communicates with the infundibulum. 



The corpora albicantia are two bodies placed behind the 

 tuber cinereum. They are composed of white matter, are 

 about the size of a pea, and contain each a gray nucleus which 

 is connected with its fellow across the median line. Each 

 is formed by the corresponding anterior pillar of the fornix. 



The posterior perforated space forms part of the posterior 

 portion of the floor of the third ventricle, and is pierced by 

 small vessels for the optic thalami. It occupies the interval 

 between the corpora albicantia, the pons, and the crura 

 cerebri. 



The crura cerebri are broader in front than behind and less 

 than one inch in length. They run from the upper border of 

 the pons to the hemispheres of the cerebrum, under the optic 

 tracts, which cross them. The fourth nerve crosses the outer 

 side, and the third issues from the inner side of each. 



Each crus is composed of two parts separated by gray matter, 

 the locus nigcr. The ventral part, or crusta, is a continuation 

 of the pyramidal fibers from the medulla and pons, while the 

 dorsal part, or tegmentum, is the continuation of the deep 

 longitudinal fibers of the pons. The crustse of the two sides 

 are entirely separate, but the tegmenta are connected at the 

 median line. 



