THE STRUCTURE OF THE KIDNEY. 



355 



outer area which looks backwards and overlies the twelfth rib and the 

 diaphragm for about its upper third, and below this the quadratus 

 lumborum. Crossing outwards and downwards behind this part of 

 the kidney the anterior divisions of the last dorsal and first lumbar 

 nerves will be seen upon the quadratus lumborum (fig. 138, p. 363). 

 When the kidney has been hardened in situ, particularly in thin 

 subjects, an indentation produced by the first two lumbar transverse 

 processes may be present near the hilum. 



Dissection. The left kidney should now be cut through from Open the 

 the inner to the outer border, and to remove the loose tissue from clean the" 



the vessels and the divisions of vessels - 

 the excretory duct. The sinus 

 containing the blood-vessels now 

 comes completely into view. 



The interior of the kidney (fig. Renal 

 136) is seen on section to con- 

 sist of an external granular or cortical and 



A _. , .. , - . . pyramidal. 



cortical portion, and of an inter- 

 nal part made of darker coloured 

 pyramidal masses converging 

 towards the centre. 



The pyramidal masses (pyra- Pyramids : 

 mids of Malpighi ; d] are from 

 eight to eighteen in number, but number; 

 generally more than twelve. The 

 apex of each mass which is free apex 

 from cortical covering, is directed 

 to the sinus, and ends in a ends in 

 smooth, rounded part, named P" 

 mamilla or papilla. In it are 

 the openings of the urine tubes, 

 which are about twenty in num- Structure ; 

 ber in each papilla, some being 

 situate in a central depression, 

 and others on the surface ; and 

 it is surrounded by one of the 

 divisions (calyx, c.) of the excre- 

 tory tube. Occasionally two of the masses are united in one papillary 

 termination. The base is embedded in the cortical substance, and base, 

 from it slender processes are continued into the cortical covering. 

 The cut surface of the pyramid has a striated appearance, owing to 

 the arrangement of the uriniferous tubules composing it, and the 

 blood-vessels. If the mass is compressed in a fresh kidney, urine 

 will exude from the tubes through the apertures in the apex. 



The cortical part (fig. 136, e) forms about three-fourths of the Extent of 

 kidney ; it covers the pyramidal masses with a layer nearly a quarter substance: 

 of an inch in thickness, and sends prolongations between them nearly 

 to their apices. Its colour is of a light red, unless the kidney is colour; 

 blanched ; and its consistence is so slight that the mass gives way consistence. 



A A2 



FIG 136. SECTION THROUGH A PIECE 

 OF THE KlDNEY, SHOWING THE 

 MEDULLARY AND CORTICAL POR- 

 TIONS AND THE BEGINNING OP 

 THE URETER. 



a. Ureter. 



b. Pelvis. 



c. Calyx. 



d. Pyramids. 



e. Cortical portion of the kidney. 



