Structure of the Pituitary 75 



fluid. In the adult human subject the cleft is generally found to be 

 obliterated or broken up into isolated cysts containing a colloid-like 

 material. The cleft is all that remains of the original tubular structure 

 of the pars glandularis, which in the early embryo was formed by a pouch- 

 like outgrowth of the buccal ectoderm (Rathke's pouch) communicating at 

 first with the cavity of the mouth, although ultimately the communication 

 has become obliterated. 



a b c d e f g h 



Fig. 45. — Mesial sagittal section through the pituitary body of an adult monkey (semi- 

 diagrammatic). (Herring.) 



a, optic chiasm a ; 6, third ventricle (infundibulum) ; e, d, extension of pars intermedia round neck of pituitary 

 e, pars anterior seu glandularis ; /. intraglandular cleft ; g, pars intermedia : h, pars nervosa. 



Traces of the original connexion with the buccal ectoderm may persist in 

 exceptional cases even in the adult, as the so-called pharyngeal hypophysis. 

 Another vestigial structure — the parahypophysis — has been described as 

 occurring in the dura mater lining of the sella turcica, and other small 

 accessory bodies similar in structure to the anterior lobe have also been 

 described. It is possible that these may undergo hypertrophy after extirpa- 

 tion of the main gland and partly supply its function. 



But the pars nervosa does not actually abut against the intraglandular 



