416 ANATOMY AND PHYSIOLOGY OF THE BRAIN. 



minute blood-vessels projecting into the ventricle. A 

 bundle of white fibres passes between the corpora striata 

 on the two sides, and two commissures, one white and one 

 grey, between the optic thalami. The lateral ventricle has 

 two prolongations, one into the olfactory bulb and the 

 other downward outward and forward into the substance 

 of the hemisphere. In the latter are noticed a large curved 

 eminence, the hippocampus major, or cornu ammonis, so 

 called from its resemblance to a ram's horn, and an elon- 

 gated white ridge, the fimbriated 'body. The fornix is a 

 triangular white structure placed between the two optic 

 thalami, and forming a portion of the floor of each ventricle. 

 It is prolonged anteriorly and posteriorly by four pillars 

 which descend into the substance of the brain. Each 

 anterior pillar turns down to join the corpus albicans, and 

 is reflected backward to join the optic thalamus. The 

 posterior pillars are connected with the corpus callosum. 

 and are continued as the fimbriated bodies. From the 

 anterior part of the lateral ventricle a small opening (fora- 

 men of Monro) leads into the third ventricle. 



The third ventricle is a cleft or interval between the two 

 optic thalami and beneath the fornix. It is crossed by the 

 three commissures of the corpora striata and optic thalami, 

 opens at its anterior part into the lateral ventricle through 

 the foramen of Monro, and at its posterior extremity through 

 the aqueduct of Sylvius into the fourth ventricle. 



Behind the third ventricle, and in front of the cerebellum, 

 are some important structures. Applied against the posterior 

 part of the optic thalami, and connected with these and 

 with the anterior pillars of the fornix by two bands of white 

 matter, is a small reddish body, the pineal gland. Imme- 

 diately behind this, and above the aqueduct of Sylvius, 

 is a large body partially divided into four by two fissures 



