146 WALTER E. DANDY and EMIL GOETSCH 



venae magna? Galeni. There is also a network of venules which 

 emerge from the posterior part of the stalk and pass over the 

 Corpora mamillaria, ending in several veins that empt}- into a 

 transverse connection between the basilar veins which forms the 

 posterior arc of the Willisian venous circle (cf. fig. 3). 



Vessels of the pars intermedia 



Certain portions of the pars intermedia are also very vascular — 

 much more vascular than the posterior lobe, though less so than 

 the anterior. It derives its circulation from three sources. The 

 thicker, tongue-like portion near the stalk, which is more or less 

 merged with the upper part of the anterior lobe, receives its blood 

 from the vessels of the stalk and from others which cross from the 

 brain substance immediately adjacent. The thin epithelial invest- 

 ment of the pars nervosa, on the other hand, is entirely devoid 

 of vessels, as Herring states. The abundant capillary network, 

 which intervenes between these two histologically different struc- 

 tures constituting the posterior lobe, does not penetrate into the 

 layers of the investing cells. The capillaries of the vascularized 

 tongue of pars intermedia, however, are in immediate contact 

 with the base of the cells and follow their villous formations. From 

 these capillary beds of pars nervosa there are two possible ways of 

 escape for the blood — upward into the veins of the stalk and base 

 of the brain, and backward into the veins of the pars nervosa and 

 thence into the circular sinus by the vascular system which re- 

 mains to be described. 



Vessels of the posterior lobe 



The posterior lobe is the least vascular of the anatomical sub- 

 divisions of the hypophysis. This is very easily recognized in the 

 fresh uninjected specimen, the anterior lobe appearing a pinkish- 

 yellow color in marked contrast to the glistening and whiter 

 posterior lobe. Injected specimens naturally bring out this con- 

 trast much more strikingly. 



