URINARY SYSTEM. 



463 



J. U U / I 



represents, not the pressure 



mination of the vascular apparatus, we can then readily 

 understand that, in the two systems of renal capillaries, the 

 pressure will not vary from that of the ordinary capillary 

 system (of the limbs, for instance). Whilst (Fig. 127) in 

 these last, on account of their intermediate position (see 

 Circulation, p. 151) between the origin of the arterial cone 

 and the termination of the venous cone, the pressure is 

 also intermediate between the two corresponding extreme 

 pressures ; that is, this pressure may be represented by T \fty 

 (that at the origin of the aorta = $&, and that of the ter- 

 mination of the vena cava = or T^T^ ; this is not so in the 

 renal system ; for this number 

 of either of the two kinds 

 of capillaries, but the pres- 

 sure of the efferent trunk 

 of the glomerulus (of the 

 vessel p V in Fig. 126) ; 

 because, as shown by the 

 diagram (Fig. 127, 2) it is 

 this efferent trunk (S P) 

 which is placed midway 

 between the distance of 

 the left ventricle (V) and 

 the right auricle (O). 



As for the pressure in 

 the renal capillaries, a similar calculation will sho,/ that in the 

 glomerulus, that is, in those capillaries which are placed between 

 the arterial system properly so called and the efferent vessel 

 (S P, Fig. 127), the pressure should be intermediate between 

 T 2 ^ and -j^, viz., -j^. In those capillaries which follow the 

 efferent vessels which wind about the uriniterous tubes to 

 give origin to the vein properly so called (Fig. 126, RC) and 

 (Fig. 127, C'C'), the pressure should be intermediate between 

 j 1 ^ and T i^, or equal to T ^ (see Circulation, p. 151). 



Fig. 127. Diagram of the two capillary sys- 

 tems in the kidney or the renal portal vein.* 



* The superposition of the numerals show that the pressures are not the 

 sortie in the capillary system of the general circulation and in each of the capil- 

 lary systems of the kidneys (at the glomerulus, and in the interstices of the 

 tubes). 



1, General circulation. V, Ventricle. 0, Auricle, a, Artery. V, Veins. 

 CC, Capillaries (pressure, 12). 



2. Renal circulation. V, Ventricle. O, Auricle, a. Renal artery and affer- 

 ent vessel of the glomerulus. (/, </, Capillaries of the glomerulus (pressure, 18). 

 $P, Efferent vessels of the glomerulus (representing the trunk of a poital vein, 

 the vessel pV of Fig. 126). c, r, Capillaries resulting from the dichotomy of 

 this efferent trunk amongst the renal tubes (pressure, 6). tf, Renal vein, cor- 

 rectly called, following this second system of capillaries. 



