ADRENAL (SUPRARENAL GLAND). 151 



cortex and the medulla of the adrenal have different origins. 

 According to Mitsukuri, the cortex is derived from the meso- 

 blast, while the medulla arises from the peripheral part of the 

 sympathetic nervous system. Gottschau believes that the 

 medulla is derived from the cortex, and that the nervous system 

 takes no part in its formation. This latter view is supported 

 by Janosik, Minot, and Inaba. Flint is of the opinion that 

 the medulla is formed separately and grows into the cortex 

 subsequently. From his description it appears that the adrenal 

 in a pig's embryo 3 cm. long consists entirely of cortex sur- 

 rounded by a delicate capsule. In its centre is a vein toward 

 which capillaries converge. By its medial surface the capsule 

 is attached to the sympathetic plexus'. Beneath the capsule 

 there appear small groups of cells, which are quite distinct from 

 the cortical cells, and form the beginning of the medulla. 

 These receive their blood supply from the capsular vessels, and 

 grow into the interior of the gland until they reach the central 

 vein. At this stage no differentiation into layers is visible in 

 the cortex. In embryo pigs 10 cm. long the zona glomerulosa 

 is first seen. The arrangement of the cells into definite columns 

 does not take place until after birth. On account of peculiari- 

 ties of this development certain variations from the normal are 

 observed in the adrenal. Islands of cortical substance may be 

 found in the medulla, and similarly small groups of medullary 

 cells sometimes are seen in the cortex. The medulla in certain 

 places may extend out to the capsule; and in other places the 

 cortex is found adjacent to the central vein. 



It is still uncertain what the exact origin of the medullary 

 cells is. They develop after the cortical cells are laid down 

 and grow in from the periphery of the cortex. They do not 

 seem to be derived from the sympathetic nervous system, 

 although the relation of the gland to this system is intimate, 

 and there are often found large numbers of ganglion cells 

 included in the cortex and medulla. 



Non-medullated nerve fibres penetrate the capsule and 

 extend in large numbers through the cortex and medulla. In 

 the cortex they give off fine branches which end on the sur- 



