i8o4 



HUMAN ANATOMY. 



ments ; but in all cases they exhibit the characteristics of sympathetic cells. Indeed, 

 so numerous are the latter that the suprarenal is regarded by some anatomists as an 

 organ accessory to the sympathetic nervous system. 



Development and Growth. — The genesis of the suprarenal body has been 

 the subject of much discussion and uncertainty, especially as to the origin of the 

 medulla. Comparative and embryological studies clearly indicate that the mam- 

 malian suprarenal body consists of two separate and distinct organs, which, although 

 intimately united as cortex and medulla, possess a different origin and function.' 



According to the investigations of 



Fig. 1526. 





Zona 

 glonierulosa 



is0- 





Capillary 



Aichel," the suprarenal in the higher 

 mammals first appears in close rela- 

 tion to the Wollftan body, the anlage 

 arising from the proliferation of meso- 

 blastic cells at the ends of invaginations 

 of the mesothelium lining the body- 

 cavity. The indi\'idual cell-groups 

 thus arising with the several invagina- 

 tions fuse into the general anlage of the 

 suprarenal. The primary close asso- 

 ciation of the latter with the Wolffian 

 body is later lost, the subsequent mi- 

 gration of the organ bringing it into 

 secondary relation with the permanent 

 kidney. 



Regarding the origin of the me- 

 dulla two views obtain. According 

 to the one generally accepted, the. 

 medullary portions are developed from 

 cells which are derived from the ad- 

 jacent embryonic sympathetic gan- 

 glia, the chief support of this opinion 

 being found in the close correspo^nd- 

 ence of the medullary cells with the 

 chromafhn elements of sympathetic ori- 

 gin occurring in other localities, such 

 cells wherever found exhibiting an 

 especial af^nity for chromium salts. 

 When fully developed, the medullar^■ 

 cells may be regarded as highly special- 

 ized cells which elaborate a powerful 

 stimulant that, when injected into the 

 blood, produces increased contraction 

 of the heart-muscle and of the invol- 

 untary muscle of the arteries. The 

 other view attributes the origin of 

 the medullary cells to the same meso- 

 blastic anlage that produces the cortical 

 cords. The differentiation of the su- 

 prarenal into cortex and medulla occurs 

 comparatively late and long after the 

 primitive organ has become sharply de- 

 fined from the surrounding tissue. For a time the entire organ consists of cells which 

 are identical in appearance. During the third month this common tissue differenti- 

 ates into cortex and medulla, in consequence of the breaking up of the outer zone into 

 columnar masses by the advent of connective-tissue trabecuLe from which delicate 

 fibrillje arise, forming the inner boundary of the cortex. Within the central part of 

 the organ thus defined numerous venous capillaries appear and break up the tissue 



' \' in cent : Journal of Anatomy and Physiology, vol. xxxviii., 1903. 

 * Archiv f. mikro. Anat., Hd. Ivi., 1900. 



Medulla 



Section of suprarenal body, showing; details of superficial 

 and deep portions of cortex. X 225. 



