§ 4 INNERVATION OF HYPOPHYSIS 65 



of blood for the pituitary. It covers the lobus intermedius and 

 the lobus anterior with anastomosing vessels, penetrating the 

 hypophysis in several places. This blood comes from a num- 

 ber of veins, which join the sinus (Fig. 52 and 53 ). A single 

 vena hypocrania bifida (n) running through the entire length 

 of the myodome is the chief source of supply of this sinus, 

 and before it splits into two branches which run around the 

 stalk, incorporates the vena afferens hypophyseos (Fig. 52x). 

 The intrahypophysial course of the blood-vessels is character- 

 ized by a rich anastomosing system of vessels in the pars inter- 

 media and posterior, whereas the lobus anterior and tuberalis 

 are less plentifully supplied with blood (Fig. 53) . The blood 

 of these capillaries soaks the glandular cells and is collected 

 in the lobus posterior into larger veins, which finally unite 

 to form the vena afferens. The arterial blood, from the stalk 

 and the carotis, eventually finds its way into this intrahypo- 

 physial system of vessels, so that the blood received leaves 

 the gland again through the large vena afferens. The course 

 of the bloodvessels points in every respect to the existence of a 

 venous system by which a slow bloodstream supplies a large 

 tissue area, carrying with it the substances needed for the 

 production of hormones and gradually charging itself with 

 the latter. Other things pointing to the existence of this slow 

 current are the marked convolution of the arteria nutricia, and 

 the funnel-shaped valves in the carotids, and also, perhaps, 

 the vascular network in the arteria infundibularis. 



§ 4. THE INNERVATION OF THE BITTERLING HYPOPHYSIS 



a. Discussion. 



Several facts indicate that the hypophysis is directed from the 

 brain. Changes following section of the hypophysial stalk in 

 animals show that the hypophysis receives nervous stimuli 

 from the hypothalamus. Excitement of the hypophysis to 

 greater activity in the spring is caused, among other things, 

 by changes in illumination and temperature. The condition 

 necessary to display and mating is, as Meltzer has shown, 

 the presence of a mussel. There is therefore no doubt that 



