260 HUMAN EMBRYOLOGY AND MORPHOLOGY. 



plexus to the medulla of the supra-renals. By the 3rd month 

 in the human foetus these cells have lost all evidence of their 

 origin from nerve cells, and have taken on a chromogenic 

 function. Probably the intercarotid and coccygeal bodies are 

 similar to the medulla in origin and nature (Swale Vincent). 



The cortical part is of quite different origin. It is developed 

 within the Wolffian ridge and causes or assists to cause, the 

 closure of the pleuro-peritoneal canal over which it is formed. 

 It arises from the endothelium covering the Wolffian ridge — that 

 part of the ridge which lies above the diaphragm in the pleuro- 

 peritoneal canal. The endothelium proliferates within the 

 Wolffian ridge and comes in contact with the medullary element 

 derived from the sympathetic. The medullary element is at first 

 the larger and surrounds the cortical ; but soon the increased 

 growth of the cortex leads to its surrounding and containing the 

 medulla. The cortical cells range themselves in rows between 

 blood sinuses. Probably cortical cells invade and replace the 

 medullary part (Minot). As the kidneys grow forwards they 

 come in contact with the supra-renal bodies which at first lie on 

 their ventral surface. The supra-renal is at first larger than the 

 kidney ; even at birth they are nearly equal in size. The nerves 

 and arteries enter the bodies on their renal surface ; the veins 

 emerge on their anterior surface. 



Isolated parts of the supra-renal body (accessory supra-renals) 

 occasionally occur in the broad ligament or in the spermatic cord 

 above the testicle. Such accessory bodies are probably derived 

 from the cortical element which is developed within the Wolffian 

 ridge and body. With the descent of the ovary and testicle, 

 which bring with them the Wolffian body, adjacent accessory 

 supra-renals, if such be present, are also brought down, and may 

 occasionally give rise to peculiar tumours. 



