BASE OF THE CEREBRUM. 85 



BASE OF THE CEREBRUM. 



Between the crura cerebri on each side and the optic 

 commissure in front is the inter-peduncular space, con- 

 taining the locus perforatus, the corpora albicantia, and 

 the tuber cinereum. 



I The locus perforatus, sometimes called the pons Tarini, 

 r posterior perforated space, is a layer of whitish-gray 

 substance, between the corpora albicantia in front, and the 

 pons Y arolii behind. It gets its name from being perforated 

 by numerous arterial twigs, intended for the interior of the 

 brain. 



The corpora albicantia are two small round bodies, placed 

 just behind the optic commissure; they are the termination 

 of the crura of the fornix. 



The tuber cinereum is a mass of gray'matter between the 

 corpora albicantia and the optic commissure; it forms the 

 floor of the third ventricle; projecting from it is a small 

 conical body called the infundibulum, which is connected 

 with the pituitary body. 



The pituitary body lies in the sella turcica, and has been 

 examined in connection with the base of the skull (p. 29). 



If the two hemispheres of the brain be gently parted an- 

 teriorly, the corpus callosum will be seen; this is the broad 

 transverse band which unites the two hemispheres of the 

 brain; it has a rounded border in front, called its genu, 

 from which it extends backward under the name of the 

 rostrum, forming a thin, concave margin, to which is joined 

 a layer of gray substance, called ^lamina cinerea, which 

 unites it posteriorly with the tuber cinereum. Laterally 

 the corpus callosum will be seen extending into the ante- 

 rior lobes of the lateral hemispheres. A band of white 

 substance, diverging on either side, crosses the substantia 

 pertbrata to lose itself at the entrance of the fissure of 

 Sylvius. The divergent processes are known as the pedun- 

 cles of the corpus callosum. The corpus callosum will be 

 further examined in connection with the interior of the 

 brain. 



The fissure of Sylvius is the separation between the an- 

 terior and middle lobes ; externally the fissure divides into 

 two parts, one of which passes before and the other behind 

 a cluster of convolutions called the island of Reil. At the 

 inner extremity of the fissure is a triangular spot, called 

 8 



