268 Susanna Phelps Gage 



Membranes. — The pia forms a complete investment for the 

 brain, but does not in all places follow the outline closely, 

 frequentl}' lying nearer the dura than the brain (Fig. i6). 

 Between the hemicerebrums the two folds unite to form a single 

 membrane within which the blood vessels run (Fig. 19). The 

 pia invests the hypophysis separating it from infundibulum 

 (Fig. 6), and is continuous over the epiphysis (Fig. 22). 

 The blood vessels in the pia are numerous, as are also the capil-- 

 laries penetrating the brain. The latter usually enter the 

 brain and return by the same path (Fig. 51), thus forming a 

 close loop, which extends deep into the alba, as at the cal- 

 losum (Fig. 51). The capillaries extend to but not into the 

 entocinerea, passing between cells of an incipient ectocinerea 

 as in the olfactory lobes and the callosal eminence (Fig. 17). 

 Plate III shows the number and extent of the loops accurately. 



Whenever the pia is separated from the brain, it is seen that 

 upon the surface of the latter nuclei indicating cells occur at 

 some little distance from one another, and that the surface is 

 clothed with filaments extending toward the pia (Fig. 51). 

 Stieda (47) found such filaments in the frog. Examination of 

 sections stained by Golgi's method, from the mesencephal, 

 where this condition is clearly defined, shows that cells lie at 

 frequent intervals among the bases of these filaments (Fig. 61). 

 The cells give off processes extending at least to the cinerea, 

 while other cells scattered in the alba give off processes 

 toward the endymal cells. In some sections the processes 

 from two cells in these different situations unite or at least 

 touch. In the larvae (Fig. 62) similar filaments are seen 

 bridging the space between the brain surface and the pia. 



The arachnoid is represented by connective tissue cells lin- 

 ing the dura, and forming a spongework in the larger spaces 

 existing between the dura and pia, notably in the triangular 

 dorsal and ventral spaces existing between the pia of the two 

 hemicerebrums (Fig. 6, 14) ; in the large spaces laterad of the 

 mesencephal (Fig. 22), and in the region of the metapore 

 (Fig. 29). 



The dura is a membrane, containing numerous large pig- 

 ment cells (Fig. 52, 55), lining the cranial cavity ; sending 



