BLOOD SUPPLY OF THE PITUITARY BODY 145 



is given off b}^ each internal carotid artery, immediately before 

 its trifurcation into the anterior, the middle cerebral and the pos- 

 terior communicating arteries. Thus, all told, from eighteen to 

 twenty or even more separate small vessels, barely visible to the 

 unaided eye, converge directly toward the infundibular stalk. 

 In addition other vessels from the posterior half of the circle of 

 Willis stream in a fine network over the corpora mamillaria and 

 converge toward the posterior surface of the infundibulum. Upon 

 reaching the stalk these vessels immediately subdivide into capil- 

 laries which empty into the dilated channels of the anterior lobe. 

 These channels are lined merely by a single layer of endothelial cells 

 which lie directly in contact with the anterior lobe cells. The sinu- 

 soidal spaces are so numerous and so large as to make the anterior 

 lobe one of the most vascular structures of the body, comprising 

 as they do a large part of the volume of the gland. Inasmuch as 

 the anterior lobe contains no arteries or veins, arterial injections, 

 owing to the large size of the granules, tend to stop at the capil- 

 laries of the stalk of the h3'pophysis. 



The injected hypophysis, view^ed in the gross by the aid of the 

 binocular, shows numerous parallel longitudinal channels uni- 

 formly distributed throughout the gland and varying slightly in 

 size. These are evidently the main channels, from which smaller 

 ones are redistributed, although histologically all have the same 

 single endothelial lining. There is, however, no very great dif- 

 ference in their size, although in specimens injected under a 

 relatively high pressure it is often possible to see very large spaces, 

 out of all proportion to the surrounding channels, owing to the 

 irregular disposition of the injection mass. 



The venous return from the anterior lobe is very similar in 

 arrangement to the arterial inflow. These channels reform into 

 capillaries and, verj' soon, into numerous small veins in the stalk, 

 from which the collecting vessels radiate to the basilar circle of 

 veins which overlies but has an arrangement very similar to the 

 arterial circle of Willis. There are six or seven of these relatively 

 large collecting trunks (fig. 3), which pass laterally and singly 

 into the basilar veins lying deep under the temporal lobe, and 

 thence upward around the crura cerebri to discharge into the 



