The Development of the Mammalian Pituitary Body 183 



The other portion of buccal epithelium (ijives rise to the anterior lobe 

 proper. The lower portion of Rathke's pouch, which is not adherent to 

 the brain, forms a solid mass of cells which grow into surrounding blood- 

 channels and into the cavity of the pouch itself. Its cells become tilled with 

 deeply staining granules and form columns without any lumen, separated 

 from one another by blood-channels of a sinusoidal character. The original 

 cavity of Rathke's pouch persists as a narrow cleft separating the anterior 

 lobe proper fi-om the epithelial investment of the posterior lobe. The cleft 

 remains a closed cavity, which varies in extent in different species and in 

 different individuals of the same species. In the cat embryo there is 

 evidence of some proliferation of cells of the anterior end of the fore-gut ; 

 these soon disappear, and do not enter into the formation of the adult 

 pituitary. 



The infundibulum is an invagination of part of the wall of the thalam- 

 encephalon which is adherent to the anterior and upper wall of Rathke's 

 pouch. It therefore possesses an epithelial covering derived from the latter. 

 The infundibular process grows backwards, and, in the cat, retains its 

 central cavity. It is lined by ependyma cells which during development 

 become elongated, so that ependyma fibres run obliquely in its neck. The 

 body of the lobe consists of ependyma and neuroglia cells and fibres ; no true 

 nerve cells are present in it, and there is very little connective tissue. The 

 posterior lobe of the pituitary is, from the first, a composite structure of 

 epithelium of the pars intermedia and of neuroglia and ependj^ma, and the 

 relations between the two tissues become more and more intimate. Its 

 vascular supply is derived from a different source from that of the anterior 

 lobe ; blood-vessels grow into it at its posterior-superior angle and form true 

 capillaries in the lobe. 



The intimate nature of the connection between the wall of Rathke's 

 pouch and the cerebral vesicle, and the maintenance of a close relationship 

 between the cells of the pars intermedia and the cerebro-spinal canal, render 

 it probable that the pituitary body of mammalia is to be regarded as the 

 representative of an old mouth opening into the canal of the central 

 nervous system. Such an arrangement exists in its simplest fOrm in the 

 Ascidian larva. A connection between Rathke's pouch or original mouth- 

 cavity and the interior of the infundibulum is sometimes seen in the 

 developing cat, and in the adult cat it is not uncommon to find epithelial 

 cells, derived from the buccal cavity, lying inside the posterior lobe in com- 

 munication with the third ventricle of the brain. The relations between 

 epithelium and nervous tissue are not accidental in the maunnalian pitui- 

 tary. The latter may have arisen, as Willey stated, from a functional 

 neuropore, but is more likely to have been produced in the manner indicated 

 by Kupffer. There is less probability of Dohrn's view being a correct 

 solution of the problem. The question is one of great interest, and is by no 

 means settled. The anterior lobe proper is a gland whose secretion must 

 enter the blood directly, and so pass into the general circulation. The pars 



