238 INTERNAL SECRETION 



The medulla consists of a mass of cells permeated by 

 blood-sinuses. The cells are irregular in shape and 

 contain granules, some of which stain brown with chromates. 

 On this account they are called ChromafiQn cells. 



Of all organs in the body, the suprarenals receive, for 

 their weight, the most abundant blood supply. The blood 

 passes through the gland from without inwards. In the 

 two outer layers of the cortex a network of capillaries runs 

 in the connective tissue, between the columns of cells but 

 not penetrating them. In the zona reticularis the blood- 

 vessels are dilated and occupy the spaces between individual 

 cells. They run into the blood-sinuses of the medulla. 



There is a liberal nerve supply, derived from the sym- 

 pathetic, filaments passing in through the cortex and 

 forming a plexus, containing ganghon cells, among the 

 cells of the medulla. 



Development and Morphology 



The cortex is of mesodermal origin, being formed from 

 the Wolffian ridge in conjunction with the primitive kidney 

 and genital gland. The human foetus is pecuhar in that 

 the cortex is abnormally large, owing to great development 

 of the inner layer or " boundary zone." After birth the 

 boundary zone degenerates, and at the same time the 

 permanent cortex develops superficially. In the an- 

 encephalic foetus the boundary zone is absent. 



The medulla is of epiblastic origin. At an early stage 

 of development certain nerve cells migrate out of the 

 spinal cord. Some of these form the sympathetic gangha ; 

 others become enclosed by the cortex of the suprarenal, 

 and form the medulla. .The former, of course, are in 

 connection with peripheral structures through their 

 post-ganghonic fibres, and w^th the cord through the 

 pre-ganghonic fibres. The medullary cells retain their 

 connection mth the cord, but assume a secretory function. 



The cells of the medidki therefore correspond to symjxithetic 

 ganglion cells. 



