YV I 



5 



SURFACE AND INTERIOR OF CEREBRUM. 91 



is called the foramen commune posterius ; it is the point 

 from which a canal, called the aqueduct of Sylvius, or Her a 

 tcrtio ad quartum ventriculum, leads backward through the 

 base of the corpora quadrigemina to the fourth ventricle, 



mpleting the intercommunication existing between all 

 he ventricles. The two lateral ventricles communicate 

 with each other transversely, and with the third perpen- 

 icularly, through the foramen of Munro, and we have just 



en how the third and fourth ventricles are connected. It 

 .8 a disputed point whether the fifth ventricle communicates 

 with the third ; if it does, it is by a very narrow orifice at 

 the angle formed by the inferior and posterior borders of 

 the septum lucidum. The weight of authority is against 

 the existence of an} 7 aperture at that point. 



The optic thalamus is a square-shaped body forming part 

 of both the lateral and the third ventricles; it forms a 

 large part of the descending cornu of the former, where it 

 presents two rounded tubercles called corpus geniculatum 

 c.rtt'rnum and internum, and is in relation, externally with 

 the corpus striatum and substance of the hemispheres. 

 Anteriorly the thalami are connected with the crura of the 

 fornix as they descend to the corpora albicantia, and poste- 

 riorly they are joined by bands from the pineal body and 

 the corpora quadrigemina. 



The pineal body is a small conical mass of a reddish 

 color and vascular character, situated above, and connected 

 by its base with, the posterior commissure; it lies between 

 the anterior pairs of the corpora quadrigemina ; it is also 

 connected with the optic thalami by white bands called its 

 peduncles. The pineal body is hollowed out into a cavity 

 containing, in addition to a viscid fluid, a quantity of 

 gritty matter called acervulus, easily detected by rubbing 

 a portion of the mass between the fingers. The pineal 

 body was supposed by Descartes to be the seat of the soul. 



The corpora quadrigemina are four small, rounded pro- 

 tuberances arranged in pairs and separated by grooves ; 

 each pair is situated on the cms cerebri of the same side. 

 The anterior pair, called the nates, are the largest ; they are 

 oblong in shape and send forward a white band to join the 

 optic thalami. The posterior pair, called the testes, are 

 rounder and whiter than the preceding, and are also con- 

 nected with the thalami by a white band. The iter a terf/o 

 ad quartum ventriculum passes longitudinally through the 

 base of the corpora quadrigemina. 



