166 



HYPOPHYSIS AND GONADOTROPHIC HORMONES 



neural lobe, and these two structures can be 

 easily separated from one another. This is 

 not a separation into anterior lobe and pos- 

 terior lobe, which terms are not applicable 

 to this type of hypophysis. 



The relation between the adenolobe and 

 neural lobe in man is unique and is described 

 in the section on the human hypophysis. 



B. HISTOLOGIC DIVISIONS OF THE HYPOPHYSIS: 

 FUNX'TIONAL PARTS 



For the purpose of correlating structure 

 with function, it is necessary to separate the 

 hypophysis into parts on the basis of inter- 

 nal structure or of function, a separation in- 

 dependent of variations in gross anatomy. 

 It matters not in theory whether the separa- 

 tion is based on fine structure or on function, 

 because one determines the other. In prac- 

 tice the exact delimitation of the functional 

 partition is determined by methods which 

 are histologic or cytologic. For the determi- 

 nation of the homology between the histo- 

 logically distinct parts of the hypophysis in 

 different species, function must be the de- 

 termining criterion. Histologically distinc- 

 tive parts in different species can be consid- 

 ered homologous and be given the same 

 name only if they are equivalent in function. 

 Nature has set a trap for those who are care- 

 less in this respect. The partition of the 

 adenhypophysis into functional parts is var- 

 iable. 



In terrestrial vertebrates the neurohy- 

 pophysis consists of two functionally distinct 

 parts (Green, 1951). Although following 

 Green in this partition of the neurohypoph- 

 ysis, I must, however, reject his terminol- 

 ogy, which used the anatomic terms "median 

 eminence" and "neural lobe" in a modified 

 sense. I propose, therefore, to use for these 

 parts the names "pars eminens'' and "pars 

 nervosaJ^ 



The two parts of the neurohypophysis 

 are: (1) Pars eininens — consists of the neu- 

 ral eminence and neural stalk and the con- 

 tinuation of this tissue in the neural lobe to 

 the point where it becomes the pars nervosa. 

 Characterized by a vascularization in com- 

 mon with the adenohypophysis. Its venous 

 effluents form portal vessels which pass into 

 and arc the main blood supply of the pars 

 anterior or the pars distalis of the adenohy- 



pophysis. (2) Pars nervosa — that part of the 

 neural lobe whose venous effluent passes to 

 the systemic veins directly. 



There are two other differences between 

 the pars eminens and the pars nervosa which 

 characterize them. First, the arteries and 

 veins of the pars eminens are confined en- 

 tirely to the surface, where they connect 

 with a rich vascular network. The interior 

 of the pars eminens is relatively sparsely 

 supplied with capillary loops — simple hair- 

 pin loops in small animals, more complex 

 vascular spikes in larger animals — which 

 penetrate it from the surface network. In 

 contrast, the arteries and veins of the pars 

 nervosa ramify within its substance and con- 

 nect with a capillary network of the usual 

 form. Second, in histologic sections the pars 

 eminens is characterized by a low content, 

 the pars nervosa by a high content, of stain- 

 able neurohypophyseal secretion. 



In most mammals, and in most other ter- 

 restrial vertebrates except birds, the parts 

 of the adenohypophysis (usual form) are 

 three. ( 1 ) Pars tuberalis — consists of the 

 adeno-eminence and adenostalk. Continues 

 distally with the pars anterior, from which 

 it is distinguished by the absence of the 

 chromophil cells which characterize the 

 latter. (2) Pars intermedia — a part of the 

 adenolobe adjacent to and adherent to the 

 neural lobe. Histologically it is character- 

 ized by the presence of cells of uniform ap- 

 pearance. These contain basophil granules, 

 in quantities that vary greatly in different 

 species. In some species granules appear to 

 be absent. Functionally the pars intermedia 

 is ciiaracterized by the presence of inter- 

 medin and of no other known hormone. The 

 pars intermedia in some species is co-exten- 

 sive with the intermediate lobe. In some, 

 e.g., the sheep and the cow (Fig. 3.4), it is 

 less extensive than the intermediate lobe, 

 and the remainder of this lobe consists of 

 pars anterior tissue (Wulzen, 1914). Such a 

 detached portion of the pars anterior is 

 known as a cone of Wulzen. In some species, 

 sucli as tlie cat (Fig. 3.5). the pars inter- 

 media is more extensive than tlie interme- 

 diate lobe, and extends somewhat into the 

 anterior lobe. (3) Pars anterior — this tissue 

 occupies the part of the adenolobe which is 

 not pars intermedia. It is characterized by 



