172 Mammalia, 



anterior lobe ; while the descending cornu traverses the 

 * middle ' lobe of the Brain, forming in its course a remark- 

 able curve round the back of what will be shown later to be 

 the Optic Thalamus. 



The Corpus Callosum will be seen to present a somewhat 

 arched form from before backwards, and to be thicker at 

 either end than in its central part. Anteriorly it forms a 

 bend or genu (of which the reflected portion is termed the 

 rostrum), and is attached to the anterior cerebral lobe ; poste- 

 riorly it is continuous with the fornix which immediately 

 underlies it ; and in the intermediate portion of its length it 

 is connected with the Septum Lucidimi (the vertical partition 

 between the two lateral ventricles). 



In the external wall of the anterior portion of the central 

 cavity will be seen a pear-shaped prominence, which also 

 forms the posterior boundary of the anterior cornu. This is 

 the Corpus Striatum^ so named from the striated appearance 

 which it presents in section. The inferior border of 

 the intraventricular portion of the Corpus Striatum is 

 bounded by a slight depression in which lie some longitudi- 

 nal fibres of white medullary substance : but these are barely 

 traceable ; however they form the Tcenia Semicircularis, which 

 anteriorly descends in close connection with the anterior pillar 

 of the Fornix, and posteriorly is continued, along with the 

 pointed end of the Corpus Striatum, into the roof of the ' des- 

 cending ' cornu. Beneath it is a large vein (Yena Corporis 

 Striati), which receives numerous smaller veins from the 

 surface of the Corpus Striatum and Thalamus Opticus, and 

 terminates in the Yena Galeni.* 



The highly vascular fringe-like membrane which comes 

 next posteriorly, extending in a curved direction across the 

 floor of the lateral ventricle, and following down the descend- 



* Vide infra, in the Velum Interpositum. 



