THE SUPRARENAL SYSTEM 131 



division of the aorta and named respectively the carotid gland and 

 Zuckerkandl's accessory organs of the sympathetic system. 



The greater number of what are usually called accessory 

 suprarenal organs are rather, from their histological structure, 

 free portions of the interrenal system, and should by rights be 

 called accessory interrenal bqdies. They are found in the neigh- 

 bourhood of the suprarenals; in the substance of the kidneys; 

 and distributed through the whole of the retroperitoneal space 

 and extending downwards into the pelvis, in women chiefly in 

 the ligamentum latum, in men in the vicinity of the spermatic 

 cord and the testicles. 



A homogeneous suprarenal is found only in the higher verte- 

 brates, and even here it is only certain portions of the two systems, 

 varying in different classes, which combine to form the apparently 

 homogeneous organ. The suprarenal of mammals, with its cortical 

 and medullary parts, represents a combination of portions of 

 the adrenal and interrenal systems. The terms " cortex " and 

 "medulla" merely represent the topographical conditions in 

 mammals ; in reptiles and birds the systems are differentiated 

 into "principal" and "intermediary columns"; in the lepido- 

 saurii and amphibia a portion of the " medullary substance " lies, 

 not in the interior, but upon the surface of the " cortex." As 

 histological definitions, " cortex " and " mectulla " are synony- 

 mous with interrenal and adrenal tissue, but being only parts of 

 these systems, they can never be employed to describe the 

 systems as a whole. 



It has been shown by means of comparative anatomy and 

 histological investigation that the bodies of vertebrates contain 

 two different and independent systems, certain portions of which 

 combine to form the suprarenals of the higher orders. This is 

 confirmed by the results of comparative embryology. In all 

 orders of vetebrates during organogenesis, two independent and 

 autonomous organic systems are evolved from two different 

 primordial beginnings. These are the adrenal and interrenal 

 organs which, according to the further development of their tissue, 

 maintain their independence either wholly or in part (as in cyclo- 

 stomata and fish). In the course of histogenesis, and after mani- 

 fold changes, large portions of each system combine to form either 

 a number of small bodies, as in the amphibia, or a single homo- 

 geneous organ, such as the suprarenals of the amniota. 



The interrenal system is the direct descendant of the meso- 

 derm. It is developed from the ventral portion, that part which 

 forms an epithelial sheath, covering the lateral plates of the ccelom 

 in the so-called interrenal zone. At about the time when the 

 sexual glands first begin to appear, thickenings of the peritoneal 

 epithelium are formed by means of mitotic cell-proliferation at 

 circumscribed areas. These thickenings take the form of buds, 

 the celts of which early acquire a characteristic appearance. Later 



