THE FULLY DEVELOPED HUMAN PINEAL ORGAN 397 



position of the cell-element, namely, wholly contained within the spongio- 

 plasm, protruding from this into a space, or completely extruded into the 

 space and connected to the surrounding structures merely by fine, taper- 

 ing processes. 



In adult specimens, however, when specifically stained for neuroglia, 

 the distinction between glial cells and the general plasmodium or syncytial 

 reticulum in which they are imbedded is quite definite, and it is at once 

 evident that the slender astrocytes and glial fibres in no sense form the 

 principal constituent of the supporting tissue of the lobules. 



The former appear as very sparsely scattered branched cells, chiefly of the 

 astrocyte type (Fig. 272, p. 403), with fine delicate processes lying in a tissue 

 which when specially 

 stained by Hortega's 

 silver impregnation 

 method is seen to be 

 principally composed of 

 branched parenchyma 

 cells which he believes 

 to be separate and in- 

 dependent units. 



By combining the 

 knowledge gained by 

 the different specific 

 methods of silver im- 

 pregnation with that 

 obtained by the best 

 nuclear and cytoplasmic 

 stains we are able to 

 distinguish in the par- 

 enchymatous tissue of 

 the adult human pineal organ three principal elements, namely : 



(1) A glial component, formed by the cell-bodies and slender branched 



processes of a relatively small number of astrocytes. 



(2) The parenchyma or pineal cells, distinguished by their large, 



pale vesicular nuclei. These are much more numerous than 

 the astrocytes and form the main bulk of the tissue. 



(3) The mesodermal elements which consist of (a) the fibrous capsule and 



trabecular, derived from the pia mater, and (b) minute profusely 

 branched cells which are present beneath the pia mater, in 

 relation with the perivascular sheaths, and distributed in 

 the lobules. These are the microglia or mesoglia cells of 

 Del Rio-Hortega, and are only clearly demonstrable by means 



Fig. 268. — Pineal Body. 



350. 



Section through the central region of the same 

 specimen as Figs. 266, 267. Two types of fibres 

 are visible, as in Fig. 267. The finer fibres appear 

 to form a network on the walls of the capillary 

 vessels. 



