THE HYPOPHYSIS CEREBRI : ITS STRUC- 

 TURE AND DEVELOPMENT 



By K. M. PARKER, D.Sc, 



University College, London 



The problems of the origin and function of the pituitary body 

 have for many years proved a stimulating subject for research, 

 with the result that a considerable mass of literature has 

 accumulated, much of which is of interest only to the specialist. 

 Stendell (19) has dealt with the comparative anatomy of the 

 hypophysis in considerable detail, but this work also is of 

 more value to the specialist than to a student of general com- 

 parative anatomy. The object of the present paper is to 

 summarise our knowledge of the hypophysis cerebri and thus 

 render it more accessible to the student of biology in all its 

 branches. 



It is impossible to give here any adequate account of the 

 work done on the hypophysis ; admirable historical notes are 

 given in papers by Herring (7), Tilney(2i), and others. The 

 literature list appended to this paper merely gives references 

 to a few out of many important publications on the pituitary 

 body. 



In the majority of Vertebrates, the primordium of the 

 hypophysis is a hollow invagination of the ectoderm, but in 

 Teleosts and Amphibia it arises as a solid mass of ectoderm. 

 It is apparent that the hollow invagination is the more primi- 

 tive type. Its position is indicated at an early stage of deve- 

 lopment (either before or shortly after closure of the brain) 

 by a thickening of the epithelium of the buccal cavity immedi- 

 ately anterior to the oral plate. This thickened area becomes 

 invaginated and retains from the first close contact with the 

 depressed region of the diencephalic floor which forms the 

 primitive infundibular recess. The lips of the invagination 

 gradually close in so that a hollow pouch-like structure, known 

 after its discoverer (17) as " Rathke's pouch," is established. 

 The opening of this pouch becomes drawn out into a narrow 



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