I.—PHYSIOLOGY 147 
and tuberalis, unite to form veins which run through the infundibular 
process to break up again into capillaries in the hypothalamus. Their 
anatomical arrangement suggests that they collect the products of the 
posterior lobe and convey them directly to the nervous tissue of this part 
of the brain. It is customary to speak of nerve ‘ centres’ and to regard 
them as subject to the direct influence of physical and chemical stimuli. 
The term ‘ centre’ is convenient, but misleading. By analogy with what 
is known of the manner of working of the nervous system stimuli act 
upon some form of receptor which is adapted to respond to a specific form 
of stimulus. The passage of material from the pars nervosa into the 
cerebrospinal fluid points to the possibility that there are such receptors 
in the diencephalon. The subcommissural organ occurs to one as a 
possible receptor, but there is no experimental evidence bearing upon its 
functions. ‘This organ, too, while highly developed in many animals, is 
not nearly so conspicuous in the adult human brain. 
CONNECTIONS OF THE PITUITARY BODY WITH THE BRAIN. 
In all vertebrates some part of the pituitary body is closely bound up 
with the floor of the third ventricle. Even in cartilaginous fishes the 
ventricle runs backward for some distance to end in the large-paired 
saccus vasculosus, and its ventral wall is invested with epithelium. In 
the mammalian pituitary abundant non-medullated nerve fibres have been 
described by Greving and by Pines. They are said to arise chiefly from 
the cells of the supraoptic and paraventricular nuclei. The fibres con- 
verge into the infundibulum, and spread out in the posterior lobe to form 
basket-like endings in the pars nervosa. Many of them penetrate the 
epithelium of the pars intermedia, and according to Croll end in knob-like 
structures in the cells. Croll points out that non-medullated fibres are 
relatively few in number in the posterior lobe which is also sparsely 
supplied with blood vessels, and regards them as secretory rather than 
vasomotor. Roussy and Mossinger also find nerve fibres arising from 
cells in the supraoptic, paraventricular and inferior hypothalamic nuclei, 
apparently secretory in function, which enter the pituitary to supply the 
pars intermedia, pars tuberalis and islands of epithelium in the pars 
nervosa. They state that lesions of the tuber cinereum must damage some 
of these fibres and thereby affect the gland. Sympathetic nerve fibres 
have also been described as entering the gland with the arteries, and Dandy 
has traced fibres from the carotid plexus along the vessels of the stalk 
and into the anterior lobe. 
Experimental work supports the view, expressed by Harvey Cushing, 
that nuclei in the diencephalon supply nerve fibres to all parts of the 
pituitary body, and exercise a controlling influence upon its secretion. 
An example of pituitary response through the nervous system is furnished 
by the observation of Fee and Parkes that removal of the pituitary of the 
female rabbit within one hour after copulation prevents ovulation, but 
later removal than this has no such inhibitory effect. It is known that the 
injection of a suitable extract of the anterior lobe of the pituitary brings 
about ovulation, and it is reasonable to infer that the stimulus of mating 
induces reflexly in the rabbit sufficient hormone for the purpose in about an 
