HYPOPHYSIS CEREBRI OF CALIFORNIA GROUND-SQUIRREL 197 



Vascularity. The pars distalis is pervaded throughout by nu- 

 merous blood sinuses. They are of varying width, and owing to 

 their elaborate distribution they come into close relation to the 

 cells. By virtue of their tortuous course, no long channels are to 

 be seen except in very thick celloidin sections, and in the usual 

 paraffin preparations they appear as irregular areas containing 

 blood. The cells of the pars distalis lie in strands or cords two 

 or three layers thick. The spaces separating them being occupied 

 by blood, it is evident that no given cell can be much more than 

 its own diameter distant from a rich blood supply. The channels 

 are lined by a well-marked vascular endothelium which inter- 

 venes between the blood and the cells (fig. 11). The arrangement 

 offers strong probability of a direct secretion into the blood 

 channels, although it is possible that the secretion is given off 

 into the tissue spaces and taken up by a perivascular lymphatic 

 system as suggested by Edinger ('11). Thorn ('01) conceives of 

 a mixed secretion from the chromophile and chromophobe 

 elements as passing into interfollicular lymph spaces. 



Surely, the vascularity of the organ is of considerable signifi- 

 cance, and it very likely plays an important part in the taking 

 up of the secretory products of the cells. In the sections which 

 I have observed in the ground-squirrel there is abundant histo- 

 logical evidence that the cells secrete into the blood stream. In 

 the region of a sinus, cells in the above-described granular stages 

 will be seen along its margins. When the blood sinus is cut in 

 cross-section the cells are seen to radiate from it in much the same 

 way as other gland cells are seen to be arranged about their 

 secreting tubules. In the deep chromophiles, which many 

 writers consider to be cells ready to discharge their secretion, 

 marked irregularities in outline may be found. These irregu- 

 larities are always found at that end of the cell bordering on the 

 sinus and separated from it only by the endothelium. In this 

 region of the cell the granules may be seen in clumps outside the 

 cell or at least exterior to the former probable limits of it (figure 

 11a). Under these conditions the cytoplasm at the irregular end 

 may be very light in granulation as compared with adjacent 

 heavily granular and smoothly outlined cells. In addition to this 



