424 STUDIES IN ADVANCED PHYSIOLOGY. 



can then be easily seen to be separated from each other by 

 a band of tissue running perpendicularly along the median 

 line of the brain from the corpus callosum to the floor of 

 the ventricles, while towards the front of the brain this 

 septum would be continuous with the septum lucidum. 



If the corpus callosum should be entirely removed the 

 entire floor of each ventricle is exposed. In the anterior 

 portion of this floor lie the corpora striata, eminences of gray 

 nerve matter each about the size of an almond. In position 

 these corpora striata lie just to the right and left of the sep- 

 tum lucidum. The floor in the posterior portion of the 

 ventricles is made by a triangular mass of white tissue with 

 its broad side towards the mid-brain and tapering towards 

 the septum lucidum. This white tissue bends abruptly 

 downward posteriorly at each side and runs to the base of 

 the lateral lobes of the brain following the ventricle in this 

 region. This broadened portion is called the hippocampiis . 

 Towards the septum lucidum this becomes gradually nar- 

 rower and where it bends downwards it is on each side called 

 \htfornix (pillar). Immediately under the fornix on each 

 side, and between it and the optic thalamus beneath is the 

 foramen of Monro already referred to. The fornices are not 

 continuous with the septum lucidum, as they seem at first 

 sight to be, but bend abruptly downwards in front of the 

 third ventricle reaching the base of the brain. Here they 

 make a sharp turn recognizable as the corpora albicantia, 

 and end in the optic thalami. 



The hippocampi are like the corpus callosum composed 

 of nerve fibers and are one of the most important bands of 

 association fibers in the brain. If by means of the scalpel 

 the fornices be cut and this entire bit of nerve fiber matter 

 lifted off or folded back there are disclosed two large bodies 

 immediately below them called the oplic thalami. The optic 

 thalami lie immediately anterior to the nates. Between the 

 optic thalami lies the third ventricle, the roof which is there- 

 fore practically formed by this band of nerve fibers just 

 removed. 



