484 



NEUEOLOGV. 



openings, the lining membrane of tlie third ventricle is con- 

 tinuous -with that of the others. 



The j)ineal gland is a small reddish-brown tubercle, placed 

 behind and above the third ventricle, in a groove between the 

 corpora quadrigemina, where it is kept in its place by a layer of 

 the velum interpositum, to which it is attached. In shape it is 

 somewhat conical, having a broad base and a free apex. The 

 base, which is turned forwards, has bands of white matter, its 



crura or peduncles, passing from 

 it to the optic thalami, which 

 they join. The pineal gland is 

 very vascular, and is constructed 

 of areolar tissue and cells, which 

 contain, besides a viscid fluid, a 

 quantity of sand-like matter {acer- 

 vulus cerebri), which gives a 

 gritty feel to the body. Though 

 these grains often accumulate 

 largely in old animals, they are 

 not regarded as the products of 

 disease. The use of this gland is 

 not known ; the ancients regarded 

 it as the seat of the soul, and the 

 chief source of nervous power. 



The corpora quadrigemina or 

 optic lobes are the four rounded 

 eminences situated immediately 

 behind the optic thalami, sur- 

 mounting the posterior part of 

 the crura cerebri, and forming 

 part of the roof of the aqueduct 

 of Sylvius. They are separated 

 by a crucial depression, and are placed one before the other in the 

 median line. In the horse the anterior pair, the nates, which are 

 grey in colour, are larger than the posterior pair, the testes, which 

 are rounded and farther apart. These bodies have connection 

 with the olivary fasciculus, and, by the crura cerebelli ad corpora 

 quadrigemina, or anterior peduncles, are joined to the cerebellum. 

 The white processes (brachia), given off from each side, pass to 

 the optic thalami and to the commencement of the optic tracts. 

 The corpora quadrigemina are ganglionic in structure, Avith inter- 



Fir.. isi 

 Entire brain opened from above— the fornix 

 and hippocampi being partly removed. « a, 

 Corpora striata , b, Body of fornix , c c, Tseui* 

 semicirculares , d d, Optic thalami , e, Pineal 

 glaud ; /, Iter ad iufundibulum , g. Opening 

 of aqueduct of Sylvius ; h h, Nates , i i, Testes 

 /; h, Anterior peduncles of the cerebflUini , 

 h k Posterior peduncles of the cerebellum ; 

 I, Valve of Vieusseus . m in , Cerebellum . n, 

 Fourth ventricle, o, Calamtis scriptorius. 



