DEVELOPMENT OF SUPRARENAL BODIES IN MAMMALIA. 19 



paired bodies derived from the sympathetic ganglia; and (2) 

 an unpaired body of mesoblastic origin. In the Amniota 

 these two bodies unite to form the compound suprarenal 

 bodies, the two constituents of which remain, however, dis- 

 tinct in their development. The mesoblastic constituent 

 appears to form the cortical part of the adult suprarenal 

 body, and the nervous constituent the medullary part." 



In view of these considerations it seemed worth while to 

 trace the development of the suprarenal bodies in Mammalia, 

 and see whether the medullary part is actually derived from 

 the sympathetic system and the cortical part from the me- 

 soblast. Accordingly, at the instance of Mr. Balfour, I have 

 been engaged in following the history of these bodies in the 

 rabbit, and to some extent in the rat. The result has fully 

 justified the conclusions set forth by Mr. Balfour in the 

 above quotations. It will be shown in this article that the 

 medullary part of the Mammalian suprarenals arise from 

 the sympathetic nervous system, totally independently of and 

 outside the mesoblastic cortical part, and becomes, in the 

 course of development, transported into the middle of the 

 cortical part, gaining only then the position which its name 

 implies. 



Before proceeding to describe the successive stages of 

 development it may, however, be well to recall here briefly 

 the essential points in the structure of the adult suprarenal 

 bodies in Mammalia. The account given below will be 

 understood to refer to the rabbit, unless otherwise specified. 

 Structure^qfjthe Adult Suprarenal Bodies. — In the rabbit 

 the suprarenals lie, usually in a large quantity of fat, at some 

 distance from the kidneys, near the opening of the renal vein 

 into the vena cava inferior, and about on a level with the ante- 

 rior end of the kidney of their respective side. The right is, 

 therefore, somewhat in front of the left, and is, moreover, 

 on the dorsal side of the vena cava, while the left is rather 

 on the ventral side. The suprarenals themselves are oval, 

 reniform, or elongated in shape, and lie with their longest 

 diameter parallel with the axis of the body. The right 

 suprarenal is often more elongated than the left, which is 

 generally oval or reniform, in the latter case having its con- 

 cave side turned towards the median line of the body. A 

 large vein is seen to enter each suprarenal at its posterior end, 

 which is a branch of the renal vein in the case of the left, 

 and of the vena cava inferior in the right suprarenal.' On 

 cutting open a fresh suprarenal, in a median longitudinal 

 plane, its division into whitish-yellow cortical part and 

 greyish medullary part becomes at once obvious. The 



