438 HISTOLOGY 



It is generally considered that the pineal body is a function! ess rudi- 

 ment. In lower vertebrates an eye-like structure develops just in front of 

 it, sometimes being found beneath a transparent cornea, but the extent 

 of the visual functions of this organ remains undetermined. The corpus 

 pineale immediately behind this eye may take its place to some extent, 

 and "often shows, as in certain lizards, traces of visual structure" 

 (Kingsley). The unimportant position to which this organ has been 

 relegated, contrasts with the familiar conjecture of Des Cartes that all 

 ideas which proceed from the five senses are perceived in the pineal body 

 as a center, and that from it all nervous impulses irradiate. In man not 

 the slightest function is now assigned to it. 



Within the pineal body, acervulus cerebri or "brain 

 sand" is usually found, consisting of round or mul- 

 berry-like concretions, 5 n to i mm. in diameter (Fig. 

 449). In specimens preserved in glycerin or balsam 

 these concretions show distinct concentric layers. They 

 consist of an organic matrix containing calcium carbo- 

 nate and magnesium phosphate, and are sometimes 

 FIG 449 ACERVULUS surrounded by a thick connective tissue capsule. 



BODY OF A WOMAN Not infrequently, especially in old age, the brain 



OU> ENT X so YEARS substance contains round or elongated bodies, distinctly 



stratified, which are colored violet by tincture of iodine 



and sulphuric acid, and therefore are related to amyloid. These cor- 



puscula amylacea are found almost always in the walls of the ventricles, 



and also in many other places in both gray and white substance, and 



in the optic nerve. They have a homogeneous capsule with occasional 



processes, and are evidently neuroglia cells transformed by amyloid 



infiltration. 



MENINGES. 



The dura mater cerebralis or dura mater of the brain, includes the 

 periosteum of the inner surface of the cranium and consists, therefore, of 

 two lamellae. The inner is like the dura mater of the cord but contains 

 more elastic fibers; the outer corresponds with the periosteum of the verte- 

 bral canal. It contains the same elements as the inner layer, but its fibers 

 run in a different direction. In order that the dura of the brain and cord 

 may be strictly comparable, some anatomists count the vertebral perios- 

 teum and the considerable layer of vascular fatty tissue beneath it, as 

 a part of the dura of the cord. In relation with the brain, the dura forms 

 reduplications extending between the cerebellum and the hemispheres, 

 and between the right and left hemispheres. Its two layers separate to 

 enclose large, thin-walled veins, the sinuses of the dura. These receive 



