1909.] 



The Functions of the Pituitary Body. 



445 



Before proceeding further it is necessary to refer to certain facts relative to 

 the structure, development, and functions of this organ. 



Development. 



Eegarding its development, it is known to have a double source of 

 formation, a hollow extension from the buccal ectoderm towards the base 

 of the brain being met by a hollow extension of the neural ectoderm 

 occupying the situation of the future infundibulum. The two extensions 

 eventually grow together and constitute the pituitary body, the buccal 

 ectoderm, which loses its connection with the alimentary tube, forming the 

 anterior lobe and pars intermedia, i.e. by far the larger portion of the organ ; 

 while the neural ectoderm becomes developed into the posterior or nervous 

 lobe. This retains in some animals its hollow connection through the 

 infundibulum with the third ventricle of the brain, although in man and 

 other Primates it becomes entirely solid.* 



' Structure. 



The structure of the parts which are thus so differently formed in the 

 embryo is also, in the adult, entirely different. For while the pars 

 nervosa s. posterior shows no development of any tissue which can be 

 supposed to possess either nervous or glandular activity — consisting as it 

 does mainly of neuroglia elements with very few vessels — the pars anterior 

 is formed of a highly differentiated epithelium-like tissue, very richly 

 supplied with large and thin-walled capillary blood-vessels, many of its cells 

 being filled with granules such as are characteristic of glandular structures. 

 The appearance of the pars anterior is, in fact, precisely that of an organ 

 which has the property of forming a secretion which is passed from its cells 

 directly into the blood-vessels, and one would, without hesitation, class it 

 amongst the internally secreting glands. 



The pars anterior in man and in most animals is separated from the 

 posterior lobe by a cleft-like cavity, which is the remains of the original 

 hollow of the outgrowth from the buccal ectoderm. But the epithelial 

 tissue immediately adjoining this cleft, and especially that which impinges 

 ■on the pars nervosa, is of a different character from that of the pars anterior. 

 The cells are less distinctly granular: they tend to be arranged in islets 

 separated by intervening tissue which is continued between them from the 



* This description of the development and structure of the mammalian pituitary body 

 is based upon the investigations of Herring (1908), which is itself supplementary to 

 and in many particulars confirmatory of the results of former observers. 



