452 SCIENCE PROGRESS 



biiccalis (including the anterior or glandular lobe and the pars 

 intermedia). The pars neuralis is poorly developed in many 

 of the lower Vertebrates, but attains considerable size and 

 importance in the higher Vertebrates, where it forms a hollow 

 or solid swollen structure, attached to the diencephalic floor 

 by a narrow neck, the pituitary stalk. The outer surface is 

 closely invested by epithelial cells derived from Rathke's 

 pouch and constituting the pars infundibularis (pars inter- 

 media " Zwischenlappe," etc.). There has been much discus- 

 sion as to whether or no the pars neuralis actually contains 

 true nervous elements. Herring (7, 8), who has dealt with 

 the pituitary body from the embryological, histological, and 

 physiological points of view, holds that the pars neuralis con- 

 sists of neuroglial cells and fibres, and, in addition, cell islets 

 derived from the pars infundibularis (pars intermedia). 



The portion of the pars buccalis which is derived from 

 sprouts from the neck of Rathke's pouch forms the pars tuber- 

 alis (Tilney, 22). In many forms there has been described 

 " an anterior tongue-like process of the pars intermedia," this 

 being a small mass of epithelial tissue produced anterior to 

 the main body of the anterior lobe, stretching towards the 

 optic chiasma and tying in contact with the tuber cinereum. 

 Tilney (22) defines the tuber cinereum as the portion of the 

 diencephalic floor which is limited anteriorly by the optic 

 chiasma, posteriorly by the corpus mammillare, and lateral^ 

 by the optic tracts. He describes the pars tuberalis in the 

 cat, dog, rabbit, rat, sheep, and fowl as encircling the pituitary 

 stalk, lying in contact with the tuber cinereum, between it 

 and the main part of the pituitary body. According to him, 

 " the pars tuberalis is moulded to the base of the brain in 

 such a manner that the saccular eminence of the tuber cinereum 

 rests in it as one saucer in another " (Tilney, 22, p. 263). This 

 description also applies to those Marsupials, 1 which I have 

 examined. Tilney regards the pars tuberalis as forming a 

 morphologically independent portion of the pituitary body 

 and its ontogeny gives support to this view. He has himself 

 described its development in the cat and chick, in both of 



1 The marsupial material to which reference is here made, as well as some 

 sections of Cyclostomata, Elasmobranchii, Amphibia, and Reptiles are all in the 

 collection of Prof. J. P. Hill, F.R.S., and I wish to express my gratitude to him 

 for his kindness in allowing me the use of his material. 



