THE BRAIN. 197 



white fibres extend backward and outward to the beginning 

 of the fissure of Sylvius. These bands are called the 

 crura, or peduncles of the corpus callosum. 



The anterior perforated spaces are limited internally by 

 these peduncles. 



The beginning 1 of the fissure of Sylvius is at the outer 

 margin of the anterior perforated space, and separates the 

 temporal from the frontal and central lobes of the cerebrum. 



The junction of the optic nerves is called the optic 

 chiasm or commissure. This junction takes place in the 

 middle line and in front of the terminus of the crura cerebri. 

 Outward and forward from the commissure projects the optic 

 nerves, while backward and outward extend the optic 

 tracts, which curve around the outer side of the crura 

 cerebri and disappear between them and the inner margin 

 of the temporal lobes. 



Behind the optic chiasm is an elevation (really depres- 

 sion) of the floor of the cerebrum called the tuber cine- 

 reum. The tuber cinereum is prolonged (downward) in 

 the shape of a funnel-shaped stalk, the infundibulum, 

 upon which or attached to which is the pituitary gland 

 (providing the brain has been carefully removed). The 

 two lobes of the pituitary body can be determined a 

 small central posterior one situated within the horse-shoe 

 shaped anterior and larger one. See Development, page 175. 



Immediately posterior to the tuber cinereum and close to 

 the middle line are two small but well-marked, rounded 

 nodules, the corpora albicantia (from their white color) or 

 mammillaria (from their resemblance to the mammae). 



Between the corpora mammillaria and the pons, and within 

 the depression between the crura is the posterior perfo- 

 rated space formed by the arteries of the posterior median 

 ganglionic system. 



