THE CHROMAFFIN BODIES AND SUPRARENAL GLAND 



369 



The Glomus Caroticum. Associated with the intercarotid sympathetic 

 plexus is a highly vascular chromaffin body known as the carotid gland. 

 Its anlage has been first observed in 20 mm. embryos. 



The Suprarenal Gland is developed from chromaffin tissue, which 

 become its medulla, and from mesodermal tissue that give rise to its cortex. 

 In an embryo of 6 mm. the anlage of the cortex begins to form from ingrow- 

 ing buds of the peritoneal mesothelium. At about 9 mm. the glands are 



FIG. 367. Section through a chromaffin body in a 44 mm. human fetus (after Kohn). X 450. 

 P, Mother chromaffin cells; sy, sympathetic cells; b, blood vessel. 



definite organs and their vascular structure is evident (Fig 201). The 

 cellular elements of the cortex are at first larger than the chromaffin cells 

 that give rise to the medulla. The anlages of the glands early project 

 from the dorsal wall of the ccelom between the mesonephros and mes- 

 entery; here they become relatively huge organs (Figs. 221, 232 and 233). 

 The differentiation of the cortex into its three characteristic layers is not 

 completed until between the second and third years. The inner reticular 

 zone is formed first, next the fasciculate zone, and last the glomerular zone 

 (50 mm.). 



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

 of the sympathetic system. In embryos of 15 to 19 mm. (Fig. 368), 

 masses of these cells begin to migrate from the median side of the supra- 

 renal anlage to a central position, and later surround the central vein 



