432 TEXT-BOOK OF EMBRYOLOGY. 



region of the cortical anlagen and then penetrate the latter in cord-like masses 

 (Fig. 388) . Finally these masses unite in the interior of the cortical substance 

 to form a single compact mass (Fig. 389) . Along with the phaeochrome masses, 

 sympathoblasts also are carried in and give rise to the sympathetic ganglion cells 

 within the gland. The two types of cells together constitute the medullary 

 substance. In the lower forms the phaeochrome masses remain separate from 

 the cortical substance and are known as the suprarenal organs. In Mammals 

 the two sets of organs (interrenal and suprarenal) unite to form the suprarenal 

 gland. 



Med. Cor. Cor. 1 



FIG. 389. Section of the suprarenal gland of a 119 mm. pig embryo. Cor., Cortex; Cor. 1 , some 

 cortical substance in the center of the gland; Med., medulla. Wiesel. 



At the time when the mesonephros is fully developed, the cortical substance 

 forms a small oval body near its cephalic end. During the union of the cortex 

 and medulla and the atrophy of the mesonephros, the suprarenal gland becomes 

 more closely associated with the cephalic end of the kidney, and by the middle of 

 the third month has practically reached its adult position. During the third 

 month and the first half of the fourth month the glands increase in size and 

 become relatively large structures, larger in fact than the kidneys. From the 

 fourth month on, they grow proportionately less than the neighboring organs, 

 and by the sixth month are about half as large as the kidneys. At birth the 

 ratio of their weight to that of the kidneys is about 1:3; in the adult about i : 28. 



While perhaps in a normal course of development all the anlagen are united 

 in the adult suprarenal gland, it is not unusual to find accessory structures in 

 various places. Some of these consist of cortical tissue only and are usually 



