Structure of the Pituitarv 



77 



cleft. It is separated from it by a layer of epithelial tissue of varying 

 thickness, which although also originally derived from the epithelium 

 of Rathke's pouch, differs in certain respects from the pars anterior — 

 its cells being less granular and its blood-vessels much less numerous. 

 This portion of the gland is known as the pars intermedia since it lies 

 between the pars anterior and the pars nervosa. From the former it is 

 separated by the cleft just described : from the pars nervosa there is not 

 always a well-defined line of separation — indeed cells of the pars inter- 



Fig. 48. — Blood-supply of the pituitary body. (Dandy and Goetsch ) A. Arterial blood-supply, 

 seen from the ventral aspect. A large number of small arteries are seen converging from 

 the circle of Willis to the neck of the gland, which has itself been removed. B. Venous 

 blood-supply. The principal veins are shown passing from the pituitary to a venous circle, 

 which roughly corresponds with the arterial circle of Willis. Both figures show the parts 

 somewhat magnified. 



media may extend for some distance into the pars nervosa between its 

 neuroglial fibres ; they impart to it an important functional significance, 

 which will be referred to later in considering the mode of secretion of 

 the pars intermedia. It is not difficult to split the gland across the middle 

 in the situation of the intraglandular cleft, thus separating the larger pars 

 anterior from the combined pars nervosa and pars intermedia. When such 

 a separation is effected the term posterior lobe has been given to pars 

 nervosa plus pars intermedia, the pars anterior being termed in contra- 

 distinction anterior lobe. 



Pars anterior sen glandularis. — As already mentioned, this is formed 

 of trabecular masses of epithelium-like cells between which are verv 

 numerous sinus-like blood capillaries lying in intimate relation to the cells, 



