THE HYPOPHYSIS CEREBRI 451 



duct, the hypophysical duct which persists until a relatively 

 late stage, when it becomes obliterated by the development 

 of the cartilaginous basis cranii. Meantime, there arises from 

 the primitive infundibular recess a short diverticulum, gener- 

 ally hollow and thin-walled, constituting the infundibular pro- 

 cess. A portion of the wall of Rathke's pouch either maintains 

 from the first or else secondarily acquires intimate relations 

 with the infundibular process. This portion may simply 

 surround the infundibular process closely, or a still more in- 

 timate relation may be brought about either by the formation 

 of outgrowths of the infundibular process which grow into the 

 surrounding epithelial tissue, or by the penetration of that 

 epithelial tissue into the substance of the infundibular pro- 

 cess. In this way the nervous portion of the pituitary body 

 and the epithelial layer directly surrounding it may become 

 so closely related as to form a single structure, commonly 

 known as the posterior lobe. From the region where Rathke's 

 pouch narrows to join the duct there arise outgrowths which 

 may take the form of a median sprout, or lateral outgrowths, 

 or a distinct proximal lobe. These outgrowths may disappear 

 (Baumgartner (2) lizards and snakes), or may grow up around 

 the rest of the pouch until they come into contact with the 

 brain and form a distinct layer of tissue lying against the 

 tuber cinereum. In some cases these outgrowths also give 

 rise to a layer of cells surrounding the main epithelial portion 

 of the hypophysis. The whole of the remainder of the walls 

 of Rathke's pouch (i.e. that which is not converted into the 

 epithelial layer covering the infundibular process, nor used 

 up in the median or lateral outgrowths), becomes converted 

 into a glandular structure. The process of conversion varies 

 considerably in different forms, even within the limits of an 

 order. It consists either in the branching of the originally 

 hollow, thin-walled pouch or in the outgrowth of hollow or 

 solid processes from the surface of the pouch, or simply in the 

 thickening of the walls, which gradually become penetrated by 

 connective tissue and transformed into a compact gland, richly 

 supplied by blood-vessels. 



The hypophysis of the adult thus consists of two main 

 parts, distinguished according to their origin as the pars 

 neuralis (nervous lobe, " Hirnteil," etc., constituting, with the 

 epithelial layer covering it, the posterior lobe), and the pars 



