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Nachdruck verboten. 



The early Development of the Circulation in the Suprarenal 



of the Bahhit. 



By Roger T, ^^tkinson, M. D. 



With 2 Figures. 



This article gives the results of a study of the early development 

 of the circulation in the suprarenal of the rabbit, beginning with the 

 first appearance of the organ and concluding with the establishment 

 of the arterio-venous circulation. It deals only with the mesenchymal 

 portion of the organ. The later development has been exhaustively 

 described by Flint (1). 



The form of circulation found in the embryonic suprarenal has 

 been described by Minot (2) and called by him "sinusoidal". It con- 

 sists essentially of a system of relatively large spaces of tubes (sinu- 

 soids) which communicate very freely with a large vein, and the endo- 

 thelial walls of which are in close apposition to the cells of the par- 

 enchyma, without the intervention of an appreciable amount of con- 

 nective tissue. Sinusoids are also found in other organs, notably in 

 the liver, pronephros and mesonephros. In the liver they constitute 

 a purely venous system throughout life. In the suprarenal, and prob- 

 ably in the pronephros and mesonephros, they become connected at 

 an early stage with the arterial system. In the adult suprarenal, the 

 sinusoidal origin of the circulation is shown by the relatively large 

 size of the "capillaries" and the very small amount of connective 

 tissue beneath their endothelium. In the amphibia the condition cha- 

 racteristic of young mammahan embryos apparently persists in the 

 adult organ (SRoiNKO, 3). 



The suprarenal first appears in rabbit embryos of about 12,5 days 

 (Harvard Embryological Collection, no. 150, sections 143 et seq.) and 

 consists of a few cords of cells lying just anterior to the mesonephros, 

 in intimate relation with several large sinusoids, which communicate 

 freely with the cardinal vein and with the sinusoids of the neigh- 

 boring mesonephros. By 13 days the suprarenal is much larger 

 (Harvard Coll. , no. 153 , sections 184 et seq.), the cells lie closer 

 together and the sinusoids are more numerous. Their endothehal 

 lining can be distinguished and they communicate very freely with the 



