THE PITUITARY BODY 



763 



of the infundibulum, into which it may be traced. It is believed that 

 the active principle of the gland is represented by this material. The 

 blood supply of the pars nervosa is relatively scanty. 



Between the pars nervosa and the intraglandular cleft above referred 

 to is a layer of cells differing from those of either the anterior or the 

 posterior lobe. This layer of cells constitutes the so-called pars inter- 

 media. The cells are somewhat like, those of the pars glandularis, except 

 that they are distinctly granular, the granules being of the neutrophile 

 variety, that is to say, they stain with neither basic nor acid dyes. Well- 

 defined vesicles containing an oxyphile colloid material are often found 



Fig. 196. Drawing from a photograph of a mesial sagittal section through the pituitary gland 

 of a human fetus (5th month): a, optic chiasma; c, third ventricle; d, pars glandularis; e, infun- 

 dibulum surrounded by epithelial cells; /, pars intermedia; g, intraglandular cleft; h, pars nervosa. 

 (Herring, from Howell's Physiology.) 



between them. The blood supply is much less abundant than, that of the 

 pars glandularis. Although well separated by the cleft from the pars 

 glandularis, the pars intermedia is not well separated from the pars 

 nervosa, because many of its cells extend for some distance into the lat- 

 ter between the neuroglial fibers. Certain of the cells in the pars inter- 

 media may be seen in various stages of conversion into globular hyaline 

 bodies, or a granular mass of material may appear in them. In either 

 case, the cells ultimately break down, setting free the hyaline or granular 

 material, which is believed to be the origin of the similar material al- 

 ready described as existing between the neuroglial fibers of the pars 

 nervosa and therefore ultimately finding its way by the infundibulum 



