ANATOMY OF THE PITUITARY BODY 



important of these changes are the formation of the neuro- 

 ectodermal plate and the process of cephalization. Very early 

 in life, and throughout development, therefore, the dien- 

 cephalic floor and the buccal ectoderm, destined to form the 

 neural and epithelial portions of the pituitary, are in contact 

 with each other. According to Gilbert (1934): 



.... Both the buccal and the neural components of the hypophysis are 

 formed as the result of the mode of development of the head region of the 

 embryo, and not as intrinsic evaginations from the stomodeal and cranial 

 epithelia. That Rathke's pouch is determined by the bending ventrally of 

 the forebrain, and that this pouch is deepened and constricted into a closed 

 vesicle by the condensation of mesenchyme around the pouch has been 

 recognized by most recent investigators. The importance of the firm ad- 

 herence of the ectoderm to the floor of the brain as the mechanical condi- 

 tion which determines the formation of a pouch in this particular region 

 was early recognized by Minot (1897), and has been further emphasized in 

 this work. This dependence of the pars buccalis on contact with the brain 

 floor has been substantiated by the experimental work of Blount (1932) 

 and Stein (1933), who showed that in both Amblystoma and chick, the 

 pars buccalis will not develop in the absence of contact with the brain 

 floor. 



.... That the place and manner of appearance of the pars neuralis, 

 and the form which it assumes can likewise be explained as due to the inter- 

 action of the growth-processes of adjacent regions on the neuro-ectodermal 

 plate seems to be equally well established by this investigation. 



.... It seems definitely clear that the original neuro-buccal adherence 

 is not destroyed at any time during the develoment of the hypophysis, but 

 its position with relation to the axis of the pars buccalis is changed by the 

 rotation of the neuro-ectodermal plate around the apex of the buccal pouch 

 as a result of growth pressures set up within the brain. This maintenance 

 of the original neuro-ectodermal adherence is the essential factor in the 

 formation of both the neural and buccal lobes of the hypophysis in the cat. 



A model of the pituitary of the rabbit at one stage of its 

 development is shown in Figure 2. This illustrates clearly a 

 phase of the development of the pars tuberalis which was 

 recognized as a separate structure by Tilney (1913). The em- 

 bryologic hypophysial stalk, from which pharyngeal hypo- 

 physial tissue may arise, should not be confused with the 

 stalk by which the pituitary is attached to the tuber cinereum 

 in postnatal life in some mammals like man. 



[3] 



