HYPOPHYSIS CEREBRI OF CALIFORNIA GROUND-SQUIRREL 199 



cell create larger triangular spaces between themselves and allow 

 for a greater inward excursion of these cell processes (fig. 4, B) . 

 The cells are compactly arranged and no sturdy bands of sup- 

 porting fibers are seen. The layer is four or five cells thick and 

 is closely applied to the pars neuralis. Toward the center the 

 layer is thinner, but where it is reflected to join the pars distalis 

 it is again thickened with the formation of the transition zone. 

 This zone, in many of the lower forms, according to Stendell, 

 usually shows a characteristic structure, but here the transition 

 is so abrupt that no such modification is apparent. 



The vascularity of this part is slight in comparison with that 

 of the pars distalis. Where in the latter lobe the tissue is richly 

 supplied with blood and where the sinuses are extremely numerous, 

 here only an occasional blood-vessel is seen, most of these being 

 near the marginal region, in which the tissue turns back to join 

 the pars distalis. As a result, the cells are not separated into 

 well-defined groups, but are distributed quite evenly throughout 

 the extent of the part. 



In addition to forming a smooth surface facing the lumen, the 

 pars infundibularis has a fairly regular neural border. No 

 elaborate granular inclusions within the pars neuralis are met 

 with. In most cases a slight undulation of the surface is all that 

 is seen. Toward the periphery of the cleft, in the transitional 

 zone, a few small inclusions occasionally occur, but by tracing 

 through adjacent sections they seem to be due to slight folds in 

 that region, and are not patches of gland tissue at all. Sepa- 

 rating the pars infundibularis and pars neuralis is a series of 

 blood-vessels, which, as mentioned by Dandy and Goetsch ('11), 

 are not concerned with the pars infundibularis. This layer of 

 vessels is thin and connective-tissue fibers are seen on either side 

 of them which apparently serve to bind together the pars 

 infundibularis and the pars neuralis. These fibers are derived 

 from the dural sheath of the brain which is prolonged down the 

 infundibulum over the nervous lobe. 



The portion of the pars infundibularis investing the infun- 

 dibulum is not very extensive. It is best seen on the caudal 

 surface of the infundibulum as a layer of cells three or four deep. 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 26, NO. 2 



