CHROMAFFIN BODIES; SUPRARENAL GLAND 



367 



The Suprarenal Gland is developed from chromaffin tissue which becomes 

 its medulla, and from mesodermal tissue which gives rise to its cortex. In an 

 embryo of 6 mm. the anlage of the cortex is present, according to Soulie, and is 

 derived from a thickening of the ccelomic epithelium. At 8 mm. the glands are 

 definite organs and at 9 mm. their vascular structure is evident. The cellular 

 elements of the cortex are at first larger than the chromaffin cells which give rise 



sy sy 



Fig. 349. — Transverse section through right suprarenal gland of a 15.5 mm. embryo (after T. H. 

 Bryce). sy, sympathetic cells; sy', groups of cells extending from the sympathetic into the suprarenal 

 gland; cap, capsule of gland; a, aorta. 



to the medulla. The anlages of the glands form projections in the dorsal wall of 

 the ccelom between the mesonephros and mesentery (Figs. 214 and 225). 



The chromaffin cells of the medulla are derived from the cceliac plexus of the 

 sympathetic system. In embryos of 15 to 19 mm. (Fig. 349) masses of these 

 cells begin to migrate from the median side of the suprarenal anlage to a central 

 position, and later surround the central vein which is present in embryos of 23 

 mm. The primitive chromaffin cells are small and stain intensely. They con- 

 tinue their immigration until after birth. The differentiation of the cortex into 



