THE ABDOMEN 817 



The medullary part is confined to the centre of the capsule in the 

 adult, is soft in consistence, and has a reddish-brown colour, due 

 to the contained venous blood. The supporting fibrous stroma 

 of the cortex pervades it, and is arranged in a reticular manner. 

 The meshes of this reticulum are occupied by cells, resembling 

 somewhat epithelial cells, and larger and more irregular than those 

 of the cortex, some of them being branched. 



Blood-supply — Arteries. — ^These are (i) the superior capsular of 

 the inferior phrenic or diaphragmatic from the abdominal aorta, 

 (2) the middle capsular from the abdominal aorta, and (3) the inferioi 

 capsular from the renal. 



The veins of each capsule eventually unite to form one supra- 

 renal vein. This vessel emerges through the hilum, and on the 

 right side it opens directly into the inferior vena cava, whilst on the 

 left side it terminates in the left renal vein. 



The lymphatics terminate in the lateral lumbar glands. 

 Nerves. — The suprarenal capsules are very richly supplied with 

 nerves, which are derived from (i) the inferior or diaphragmatic 

 plexus from the semilunar ganglion of the solar plexus, (2) the 

 suprarenal plexus from the semilunar ganglion and coeliac plexus, 

 and (3) offshoots from the renal plexus. According to Bergmann, 

 the suprarenal capsules also receive fibres from the phrenic and 

 pneumogastric nerves. The fibres, which are chiefly non-medullated, 

 form rich plexuses in the medullary part, where they have numerous 

 ganglion cells connected with them. 



Development. — The suprarenal capsule makes its appearance internal to 

 the Wolffian body. The cortex is of mesodermic origin, and the medulla is 

 developed from the ganglia of the primitive abdominal sympathetic chain. 



The cortex is developed from cellular outgrowths of the mesotheUum of 

 the coelom or body-cavity, on the mesial aspect of the mesonephros, or Wolffian 

 body. These outgrowths soon become separated from the ccelomic meso- 

 thelium, and unite to form a soUd mass, which constitutes the cortex. 



The medulla is derived from the ganglia of the primitive abdominal sympa- 

 thetic chain. Groups of cells grow out from the gangUa (these cells being 

 consequently of ectodermic origin), and they invade the cortex. They lose 

 their connection with the sympathetic ganglia, and become differentiated 

 into two groups. The cells of ope group are chromaffin cells, and stain a dark 

 yellow colour with chromic acid salts. The cells of the other group are 

 ganglion cells. All the cells developed from the sympathetic ganglia gradually 

 pass to the centre, where they constitute the medulla. 



The suprarenal body thus develops in two parts — cortex, derived from the 

 ccelomic mesothelium (mesoderm), and medulla, derived from the abdominal 

 sympathetic gangUa, and therefore of ectodermic origin. 



Structure of the Kidneys. 



The kidneys are compound tubular glands. Each organ is in- 

 vested by a capsule, composed of fibrous tissue with a certain 

 amount of elastic fibres. The deep surface of this capsule is 

 attached to the peripheral portion of the renal substance by fine 

 fibrous processes and small bloodvessels. Underneath it there 

 is a certain amount of plain muscular fibre-cells, arranged in a 

 somewhat plexiform manner. At the hilum on the inner border it 



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