THE DUCTLESS GLANDS 401 



Rathke's pocket) is preserved in Polyp terus, and Cyclostomes. 

 In the latter, however, the duct has given rise to the large 

 hypophysial sac which extends beneath the brain and has lost 

 contact with the pituitary body. At the next stage in its 

 evolution it must be imagined that the gland entered into 

 relations with the infundibulum of the brain, and that it adopted 

 the method of secreting into the blood-stream. 



The functions of the pituitary are many, and they are only 

 very imperfectly known. It must suffice to say that among 

 these functions are those of : promotion of growth, control of 

 blood-pressure, causing contractions of the uterus, expanding 

 the black pigment-cells in the skin of amphibia, and stimulating 

 the mammary glands to secrete milk. 



The Adrenal. — Like the pituitary, the adrenal bodies of 

 the Tetrapods are composite structures. They are made up 

 of an external cortex derived from the (mesodermal) coelomic 

 epithelium, and a central medulla (chromafrlne tissue, so-called 

 from its staining reactions) derived from the (ectodermal) cells 

 which have migrated out from the nerve-tube in connexion 

 with the sympathetic nerve-cells. In the fish, these two 

 components are quite separate. The cortex of the adrenal is 

 in them represented by the inter-renal, which, as its name 

 implies, is situated between the kidneys. The medulla is 

 represented by a number of supra-renal bodies which lie on 

 or near the sympathetic nerve-chains, on each side of the aorta ; 

 they are roughly segmental in arrangement. In the Cyclo- 

 stomes, the supra-renals are closely associated with the 

 ganglia of the dorsal roots, but the inter- renals are not well 

 known. 



Coming to the Tetrapods, the inter-renals and supra-renals 

 are fused together to form the adrenal bodies, but in the more 

 primitive forms such as the newts, these still resemble the fish 

 in that they are not compact but form separate strips extending 

 along the sympathetic nerve-chains, from the kidney to the 

 anterior region of the thorax. The carotid gland, which is 

 situated at the joint of the internal and external carotid arteries, 

 is one of these. 



The secretion of the medullary portion of the adrenal 



2 D 



