346 THE DUCTLESS GLANDS 



first, a composite structure of epithelium of the pars intermedia 

 and of neuroglia and ependyma, and the relations between the 

 two tissues become more and more intimate. 



The early stages of development of the Elasmobranch 

 pituitary resemble those in the mammal, except that there is 

 no invagination of the wall of the cerebral vesicle in Elasmo- 

 branchs to form an infundibular lobe. The body is derived 

 entirely from the buccal epithelium of Rathke's pouch. 



The relation of the pituitary to the brain ventricles is similar 

 to that in higher vertebrates, but this is accounted for by the 

 development of a paired saccus vasculosus, each of which 

 pours its secretion into a common infundibular canal. The 

 wall of this is lined with epithelium similar to that lining the 

 saccus vasculosus. Its nervous structure is lost, being replaced 

 by connective tissue and numerous thin- walled bloodvessels. 

 There is no invasion of the wall of the canal by epithelial cells, 

 and no hyaline bodies are formed. 



The pituitary body of the Elasmobranch is a gland, the 

 secretion of which is poured directly into the bloodvessels. 

 There is no evidence of any direct secretion by the pituitary 

 into the brain ventricles. 



C. Older Views as to the Functions of the Pituitary 



Body 



The oldest theory concerning the pituitary body is trans- 

 mitted by, and survives in, the name the organ bea'rs. The 

 secretion of the mucous membrane of the nose (pituita) was 



^supposed to be derived from the " glandula pituitaria." This 

 was the view of Galen, held also by Vesalius. At the period of 



/ Vieussens and Sylvius, the body was supposed to have to do 

 with the formation of the cerebro-spinal fluid. 1 



Gushing calls attention to a remarkable paper by Lower 



/ (Dissertatio de Origine Catarrhi, 1672), who was the first experi- 

 mentally to disprove the Galenic doctrine. " For whatever 

 serum is separated into the ventricles of the brain and tissues 



1 It is interesting, as pointed out by Gushing, to note that a substance 

 from the gland may under certain conditions enter the nose, ami that. 

 according to modern conceptions, the pituitary body does add something to 

 the cerebro-spinal fluid. 



