INTERNAL PARTS. 549 



and is seen only on section of the hemiepbere. Its horizontal section re- 

 sembles that of a biconvex lens, being wider in the centre than at either 

 end, hence its name. Its antero-posterior diameter corresponds closely 

 with that of the Island of Reil, and its greatest width is opposite the 

 anterior edge of the optic thalamus. On a transverse vertical section 

 through the middle it appears triangular, the apex of the triangle 

 being directed inwards, and two clear lines, parallel to the outer side, 

 divide it into three zones, of which the outer is striated and the inner 

 slightly reddish in tint. On its outer side is the grey lamina, termed 

 the daustrwn (p. 504). 



Along the inner border of each corpus striatum, and in a depression 

 between it and the optic thalamus, is seen a narrow whitish semitrans- 

 parent band, named Umia semicircular is, or stria terminalis (fig. 383, c), 

 which is continued backwards into the white substance of the roof of 

 the descending cornu of the ventricle. In front it reaches the corre- 

 sponding anterior pillar of the fornix, and descends in connection with 

 that cord of white substance. 



The thalami optici {jiosterior cerebral ganglia) {d, fig. 383) are of an 

 oval shape, and rest on the corresponding cerebral crura, which they in a 

 manner embrace. On the outer side each thalamus is bounded by the 

 corpus striatum and taenia semicircularis. The upper surface, which is 

 Avhite, is free and prominent, and is partly seen in the lateral ventricle, 

 and partly covered by the fornix. Tlie part which is seen in the lateral 

 ventricle is more elevated than the rest, and is named the anterior 

 tubercle. The posterior and inner part of the upper surface, beneath the 

 fornix, is likewise prominent and is termed the posterior tubercle {pul- 

 mnar) (th, in fig. 384). The posterior surface, which is also white and 

 free, projects into the descending cornu of the lateral ventricle. The 

 inner sides of the two thalami are in partial contact one with the 

 other. They present grey substance uncovered with white, and are 

 generally connected together by a transverse portion, which forms the 

 middle or soft commissure of the third ventricle. According to Mey- 

 nert, the grey matter on the inner surface is distinct from that of the 

 interior of the thalamus. 



The pineal body or gland (conarium) (fig. 383) is a smau reddish 

 body, which is placed beneath the back part of the corpus callosum, and 

 rests upon the anterior elevation of the corpora quadrigemina. It is ad- 

 herent to the under surface of the velum interpositum, so that it is liable 

 to be torn away from the brain in removing that membrane. It is about 

 the size of a small cherry-stone. Its base of attachment, which is its 

 broader part, is directed forwards, and is connected with the rest of the 

 cerebrum by white substance. This white substance is principally 

 collected into two small rounded bundles, named peduncles of the pineal 

 gland (fig. 384, sp), which pass forwards upon the optic thalami along 

 their upper and inner borders, and may be traced as far as the anterior 

 pillars of the fornix, in conjunction .with which they descend. These 

 peduncles are connected with each other behind, and the band of union 

 between them is adherent to the back of the posterior commissure. 



The pineal gland is very vascular. It is hollowed out into two or 

 more cells, which, sometimes at least, open anteriorly into the ventricle, 

 and almost always contain, beside a viscid fluid, many round and 

 angular corpuscles densely massed together, and a quantity of gritty 

 matter, named acervulus cerebri. This consists of microscopic round 



