THE CEREBRUM. 367 



dal body, the long diameter of which is transverse, and amounts 

 to three or four lines, while the short diameter is about three 

 lines. These diameters are> however, sometimes reversed. The 

 substance of the pineal gland is cineritious and of a reddish co- 

 lour. At its inferior part there is a small cavity, sometimes 

 lined with medullary matter, and the orifice of which looks to- 

 wards the third ventricle. 



This body is connected to the adjacent parts by several cords. 

 From its bottom there proceeds, on each side, the long medul- 

 lary filament, called its peduncle, which runs along the upper 

 internal face of the thalamus opticus, and, as observed, joins, or 

 is continuous with, one of the filamentous processes from the 

 Eminentia Mammillaris. From its base there proceeds a trans- 

 verse lamina of medullary matter, called the Posterior Commis- 

 sure of the brain, which first advances forwards, and then re- 

 cedes, so as to be in some measure doubled on itself. This la- 

 mina, at either end, is united to the upper posterior part of the 

 corresponding optic thalamus, and by its lower margin runs into 

 the superior edge of the tubercula quadrigemina. 



Frequently, within the pineal gland, and sometimes on its 

 surface, there is an accumulation of calcareous matter, the Acer- 

 vulus Cerebri, that appears about the sixth year f life, and con- 

 tinues for ever afterwards. It is variable both in quantity and 

 in its mode of concretion, for sometimes there are only a few 

 atoms of grit, scarcely distinguishable by the feel; while, on 

 other occasions, it is collected into a body of irregular shape, 

 and more than a line in diameter. The pieces of which the 

 acervulus consists are sometimes united by cellular substance, 

 and enclosed in a sac. The chemical analysis presents phos- 

 phate of lime in large proportion, carbonate of lime, and ani- 

 mal matter. 



A reflection of pia mater, called the Velum iBterposilum, se- 

 parates the pineal gland from the fornix, and the fornix from 

 the thalami nervorum opticorum. 



The Tubercula Quadrigemina (or the Nates et Ttstes) are 

 situated on the superior face of the crura cerebri, and just be- 

 hind the thalami nervorum opticorum. A very complete view 

 of them is obtained by separating the posterior lobes of the ce- 



