22 Journal of Comparative Neurology. 



small roundish body, which stands in so close relation to the 

 brain membrane that it is removed with it ; this is the so-called 

 glandula pinealis. In the same article under the caption "Das 

 Epithel der Hirnventrikel und die Plexus Choroidei," he further 

 describes the pineal and plexus : by the combination of the 

 pia mater and the epithelium is formed the so-called plexus 

 choroidei. There exists a plexus choroideus of the fourth ven- 

 tricle, one of the third, and in close connection with the latter 

 the two plexus choroidei of the "Lobi hemisphaerici." There 

 exists no distinct epiphysis cerebri (glandula pinealis) in turtles ; 

 the small cuneiform body which covers the third ventricle and 

 roof of the diencephalon and is intercalated between the pos- 

 terior sections of the lobi hemisphaerici, is found upon micro- 

 scopic investigation to be nothing other than the plexus cho- 

 roideus of the diencephalon or of the third ventricle ; nervous 

 elements are wanting. It sufficies to say that the plexus does 

 not lie immediately on the diencephalon nor on the third ven- 

 tricle, but high above them. Farther cephalad where the third 

 ventricle enters the foramen of Monro the plexus passes from 

 the diencephalon into the unpaired ventricle of the forebrain and 

 then passes laterally through the foramen of Monro into the 

 lobi hemisphaerici. In their structure all plexus choroidei are 

 similar: they consist of folds or projections of the pia, which 

 are covered with epithelium. Between the folds and in the 

 projections of the pia are bloodvessels. The epithelium is in 

 continuous connection with the epithelium of the ventricle ; 

 we see this most clearly in the fourth ventricle. The epith- 

 elium is always one layered ; the cells are polyhedral and 

 irregular, have a diameter of .015 mm., granulated protoplasm 

 and round nuclei. The cells of the plexus have no cilia. 

 Stieda describes the pineal of the mouse as surrounded with a 

 connective tissue covering from which delicate septa penetrate 

 into the interior, to form a fine network. In the meshwork of 

 reticulum are found large, granulated, irregular cells, whose 

 contour is very indistinct, so that the densely crowded cells are 

 often inseparable and present the appearance of a uniformly 

 granulated mass filled with scattered nuclei. 



