THE DEVELOPMENT OF THE MAMMALIAN PITUITARY AND ITS 

 MORPHOLOGICAL SIGNIFICANCE. By P. T. Herring. (From 

 the Physiology Department, University of Edinburgh.) 



{Received for imhlicilion Wth February 1908.) 



Introduction. 



The development of the pituitary body has been a favourite subject of 

 research by embryologists. Its position in the embryo, forming as it were 

 a meeting-point for the anterior end of the neural canal, buccal invagination, 

 archenteron, and notochord, gives to the pituitary an importance, the signifi- 

 cance of which has been the object of much speculation. Some authorities 

 have looked upon its relations to these structures as more or less accidental ; 

 others have attached great weight to them. Kupf f er, indeed, regarded the 

 pituitary body as an important key to the phylogeny of the vertebrate head. 

 The morphological significance of the pituitary is also of interest from a 

 physiological point of view, and some of the theories which have been 

 advanced regarding it will be briefly discussed in this paper. 



Nearly all the work that has been done on the development of the 

 pituitary body has been concerned with its mode of origin and ^^^th the 

 early stages of its growth. The later stages, although probabl}^ of greater 

 physiological importance, have been comparatively neglected. The difier- 

 entiation of the epithelium of the anterior lobe, the relations of epithelium 

 to the nervous tissue of the posterior lobe, and the extraordinary difierences 

 in the vascularity of its several parts are all features which need investiga- 

 tion. Its development in mammals has been followed chiefly in animals in 

 which the posterior lobe of the pituitary becomes a solid structure at a 

 comparatively early stage. In the cat, this lobe remains hollow throughout 

 development, and presents peculiarities of morphological interest which are 

 not found in the pituitaries of other animals. The structure of the posterior 

 lobe in the cat is also of a simpler character, and the nature and arrange- 

 ment of the cells found in it can be interpreted more readily than in the 

 case of those animals which possess a solid lobe. For these reasons the 

 pituitary body of the cat forms the basis of the description in this paper. 

 The embryos of man, ox, and pig, which furnish a ditt'erent type of pituitar}^ 

 have also been examined, and some of the more important features presented 

 by them receive attention. 



