THE KIDXE Y AXD URINAR Y PASS A GES. \ 7 r 



glomeruli and blood-vessels. Later, in making the injection, 

 the narrower passages of the medullary rays become filled, and 

 at last the lymphatics of the medullary substance itself. The 

 whole reminds us of the arrangement in the testicle (see be- 

 low). True lymphatics with valves first appear, however, at 

 the hilus. 



The question now arises, which of the two systems of ves- 

 sels, that of the glomerulus or the net-work circumvoluting 

 the uriniferous canals, secretes the urine ? This role has been 

 assigned to the glomerulus, and only the signification of an 

 absorbing arrangement ascribed to the capillary net-work of 

 the uriniferous canals (Ludwig). According to another view 

 (Bowman), however, the glomeruli secrete the water chiefly, 

 and the cells of the uriniferous canals, as true gland cells, fur- 

 nish the characteristic solid constituents of the urine, which 

 are washed out by the water flowing past. A new, and as I 

 can say correct, observation of Heidenhain's is of signifi- 

 cance for this theory of Bowman's. Indigo sulphate of soda 

 injected into the veins of a living mammal is not excreted by 

 the glomeruli, but through the convoluted glandular canals 

 of the cortical pyramids. 



Let us finally take a hasty glance at the passages which 

 convey away the urine. 



The calices and pelvis of the kidney present a connective- 

 tissue outer layer, a middle layer of crossed smooth muscles 

 (especially in the pelvis of the kidney), then a mucous mem- 

 brane with the pavement epithelium mentioned at p. 30. 

 Mucous glands may also occur. 



The muscular coating is thicker in the ureter. An external 

 layer shows longitudinal, and an inner layer transverse fibres. 

 Further downwards, a third, innermost, longitudinal layer is 

 added. The urinary bladder has a relative structure. The 

 muscular layer, considerably thickened, consists of oblique 

 and transverse reticularly connected bundles of fibres. The 

 sphincter vesicae appears at the neck of the bladder as a 

 thicker annular layer. The longitudinal layers of the detru- 

 sor urinoe run over the vertex and anterior wall of the organ. 



