68 G. W. Harris 



forcibly removed from the skull the median eminence often tears away from 

 the hypothalamus and remains attached by the stalk to the sella turcica and 

 its contents. After hypophyscctomy or pituitary stalk section the portal 

 vessels thrombose and the median eminence is clearly defined as a hard 



Hypothalamus 



Nerve 

 tracts 



Mediam 



Portal 

 vessels 



Neural 



lobe 



Anterior 



lobe 



Fig. 6. To show the region — the median eminence — probably involved in the transfer of 

 humoral agents from hypothalamic nerve tracts to the hypophysial portal vessels. 



plum-colored nodule whose vessels have undergone retrograde thrombosis 

 (Fig. 7). Since the median eminence is structurally part of the neurohypo- 

 physis (and forms about 12% of total neurohypophysial tissue — see Campbell 

 and Harris, 14), many workers have investigated the effect of posterior 

 pituitary extracts on anterior pituitary activity. A priori there would appear 

 to be little to support this procedure, since — firstly, the median eminence : 

 anterior pituitary complex is evolutionarily the basic unit, with the neural 

 lobe arising as a secondary outgrowth from the median eminence in terrestrial 

 forms (38); secondly, the median eminence in all probability contains nerve 

 tracts with their fiber terminations and chemical constituents that are not 

 present in the neural lobe; and thirdly, although the median eminence is 

 constantly connected to the adenohypophysis by a rich vascular unit, the 

 neural lobe is connected by scanty capillaries at most. Some authors have 

 laid emphasis on the existence of these capillaries, but there is little data that 

 they possess much functional significance and, indeed, in some mammals 

 (whale, porpoise, sea-cow, armadillo, Indian elephant) and birds the two 

 lobes of the pituitary are separated by an intervening fibrous septum. Thus 

 although there is much data that the median eminence of the neurohypophysis 

 is directly related to anterior pituitary function there are few reasons for 

 believing the neural lobe of the neurohypophysis is so related. 



Some reports in the literature have dealt with the effects of extracts of the 

 hypothalamus (presumably including the median eminence) on anterior 



