110 EQUINE ANATOMY. 



rior pillars, ending in the hippocampus, in front by two similar 

 ones, which form the corpus albicans. They form the anterior 

 boundaries of the foramina of Monro. 



The hippocampi are nuclei of gray, covered with white matter, 

 on the floor of the lateral ventricle. They are formed by the 

 bending in of the convolution above the corpus callosum and 

 present a flattened border, the corpus fimbriatum. 



The corpus striati are projections on the floor of the lateral 

 ventricles, of gray and white tissue in lamellae. They are sepa- 

 rated from the thalami by long bands, the t(zni<z semicirculares. 

 They are divided into two parts, the intra-ventricular and extra- 

 ventricular nuclei. 



The choroid plexus is a process of the pia that passes in by the 

 great transverse fissure, becomes the velum interpositum, passes 

 from the lateral to the third ventricle and beneath the fornix. 

 Their veins form the vena galeni, which end in the sinus of the 

 falx. 



THE THIRD, OR VENTRICLE OF THE THALAMI OPTICI. 



Boundaries. 



Roof, optic thalami meet together. 



Floor, lamina cinerea. 



Sides, optic thalami and peduncles of pineal gland. 



Communications . 



In front, foramen of Monro with lateral ventricles. 



Behind, the iter a tertio ad quartum ventriculum, or aqueduct 

 of Sylvius, passing under the corpora quadrigemina to end in the 

 fourth ventricle. 



Running across the cavity are also seen the anterior white com- 

 missure between the corpora striata, and the posterior white 

 commissure between the thalami, behind. The gray commissure 

 is simply the coming together of the thalami forming the roof. 



THE FOURTH, OR CEREBELLAR VENTRICLE (see Medulla). 



Boundaries. 



Roof, valve of Vieussens and cerebellum. 



Floor, medulla and pons. 



Sides, restiform body and processus e cerebello ad medullam. 



Anteriorly, continuous with aqueduct of Sylvius. 



Posteriorly, summit of calamus scriptorius. 



