THE URINARY SYSTEM: KIDNEYS 4x7 



the organ where the latero-ventral face presses against the ventral peritoneum. The 

 serosae of the two kidneys are continuous with one another across the roof of the body 

 cavity and form a broad sheet of connective tissue (Fig. 22 m) under which, in ventral 

 view, lie the aorta and postcava. 



The serosa and capsula are continuous with the connective tissue laminae of the 

 interior of the kidney along a line running down the centre of the mesal face of the kidney 

 from the point of entrance of the blood vessels to the posterior emergence of the ureter. 

 There is an involution of the fibrous investments along this line (Figs. 23, 24, 25 c), so 

 as to form a horizontal sheet within the kidney dividing its contents into two separate 

 ventral and dorsal parts. 



The structure of the kidney 



The kidney is a composite body. It is made up of a great number of little kidneys 

 bound together by the above fibrous investments. The little kidneys will be called 

 "renculi", following the practice of Daudt and Beauregard and Boulart. Owen, how- 

 ever (1868, vol. in, p. 608), gives to them the name "renule". In the adult each 

 individual renculus is a complete unipyramidal kidney, with cortex, medulla, pelvis and 

 calyx, and with its own arterial and venous blood system — exactly similar to the whole 

 kidney of other mammals. The general disposition of the renculi is in groups (lobules) 

 of as many as five or six. This, however, becomes less distinct in older kidneys as the 

 renculi increase in size. 



Scattered apparently at random throughout the substance of the kidney, renculi occur 

 which are joined in pairs and occasionally in threes. Two types of conjoined renculi 

 have been distinguished as follows: 



(i) Renculi joined by their cortices and medullae. 



(ii) Renculi joined by their medullae with their cortices free. 



A fibrous septum is visible between the two members of a pair, continuous with the 

 tunica albuginea and extending down as far as the junction of the cortical or medullary 

 tissue. A part of the main arterial system of the renculus is always included in this 

 septum. The septum completely separates the capsules and tubules of one member of 

 the pair from those of the other, and there is no sign of any splitting of the tubules or 

 capsules themselves around the line of separation. Externally upon the surface of the 

 renculi an efferent vein follows the suture marking the line of separation between the 

 members of the pair. The pelves and papillae of these conjoined renculi are nearly 

 always separated from one another: only rarely were paired renculi found in which there 

 appeared to be two joined papillae in one pelvis. 



Beauregard and Boulart considered that the apparently paired and occasionally 

 triplicated renculi should be regarded as the result of fusion of neighbouring renculi, 

 but Daudt believed them to be the result of fission. There is, however, no sign of 

 fission of the actual capsules and tubules themselves, such as might be expected along 

 the line of separation of the members of a pair if a process of division were going on. In 

 all foetal kidneys these renculi are found paired and triplicated from their earliest 

 origin, so that it would appear that they arise in this condition from the beginning. As 



