PITUITARY 23 



clear that the old rather coarse subdivision of the organ into three 

 parts — pars anterior, pars posterior and pars intermedia — is no 

 longer sufficient for accurate description. The pars posterior has 

 a central part continuous with the hypothalamus, and an outer 

 epithelial covering (pars intermedia) continuous with similar cells 

 in the anterior lobe. Further, a thin zone is spread out from the 

 pars anterior at the base of the brain ; this is the important 

 pars tuberalis that was overlooked for many years. The pars 

 anterior or pars distalis differs very little in its structure in different 

 types of mammals. Essentially it consists of columns of cells 

 lying between large vascular sinuses and a very small amount of 

 connective tissue. The chromophile cells of this part stain 

 intensely on account of the presence of very large numbers of 

 granules in their cytoplasm. Two types of granules are present, 

 known as beta and alpha ; the former tend to stain with basic, 

 and the latter with acid stains, but this is not really a specific 

 character ; there is, however, little doubt that the two types of 

 granules are never found in one cell, and equally transitions from 

 the one to the other form are not known. In man there seems to 

 be no orderly arrangement of the two types of cells, although the 

 alpha ones are much the more numerous. These granules are 

 large and almost completely fill the cell, whereas the beta form are 

 smaller and less distinct and lie in rather larger elements than do 

 the alpha granules. The Golgi apparatus lies in a clear area near 

 the nucleus, and is more easily seen in the beta cells on account of 

 the paucity of granules ; equally mitochondria are more easily 

 seen in this type of element. 



Then we have to mention the so-called chromophobe cells, 

 which are non-granular. These elements also are of two types ; 

 first the smaller form, known as chief or reserve cells. Then 

 there are larger elements, often near the middle of the columns, 

 in which a complex reticulum may be seen. These are sup- 

 posed to be chromophile cells from which the granules have 

 been lost. 



The pars intermedia is almost non-vascular and also contains 

 two types of cells. First, elongated narrow cells stretching the 

 whole width of the pars intermedia, and easily impregnated by 



