300 HUMAN ANATOMY. 



The roof, by the velum interpositum, suspending the choroid plex- 

 uses of the third ventricle, and laterally the peduncles of the pineal 

 gland; floor, by the parts inclosing the interpeduncular space at the 

 base of the brain, viz.: the lamina, cinerea, tuber cinereum and infundibu- 

 lum, corpora albicantia and the posterior perforated space ; laterally, by 

 the optic thalami; in front, by the anterior commissure and anterior 

 crura of the fornix; behind, the posterior commissure and the Her a 

 tertio ad quartam ventriculum. 



THE FOURTH VENTRICLE is a diamond-shaped cavity between 

 the cerebellum behind and the posterior surface of the medulla 

 oblongata and pons in front. It is inclosed behind by the pia 

 mater, which contains an opening for the exit and entrance of 



Ch.roiJ . ._,_. 



o 



Kcess of Iff Vent 



FIG. 137. 



Mesial section of brain and brain stem. 1, anterior commissure; 

 2, middle commissure; 3, posterior commissure; 4, pituitary body; 

 IV, fourth ventricle. 



the subarachnoid fluid from the subarachnoidean space of the 

 brain and spinal cord, and a vascular fold of pia mater the 

 choroid plexus. It communicates in front with the third ven- 

 tricle by the iter a tertio ad quartam ventriculum. It is bounded 

 as follows : 



The roof, valve of Vieussens and the cerebellum, containing in front 

 the foramen of Magendie, by which it communicates with the subarach- 

 noidean space; the floor, the posterior median fissure of the medulla 

 and pons, the fovea posterior, the orifice [ventricle of the central canal 

 of the cord] of Aurantius, the locus cceruleus, and the ttenia violacea, 



