THE KIDNEYS 



1351 



AREA CRIBROSA 



EXCRETORY 

 TUBULES 



WALL OF RENAL CALIX 



FlG. 1095. Area cribrosa of renal papilla. (Toldt.) 



SUPERIOR 

 EXTREMITY 



constitutes the pararenal fat or body. The kidney is held in position through the 

 attachments of the fascia renalis and by the apposition of the neighboring viscera. 



General Structure of the Kidney. 



The kidney is invested by a capsule of 



interlacing bundles of fibrous connective 



tissue (tunica fibrosa), which forms a firm, 



smooth covering for the organ. The cap- 

 sule can be easily stripped off, but in doing 



so, numerous fine processes of connective 



tissue and small bloodvessels are torn 



through. Beneath this coat, a thin wide- 

 meshed network of unstriped muscle fibres 



forms an incomplete covering. When the 



capsule is removed, the surface of the 



kidney is found to be smooth and even, 



and of a very deep red color. In infants, 



fissures extending for some depth may be 



seen on the surface of the organ, a remnant 



of the lobular construction of the gland 



(Fig. 1105). The kidney is dense in 



texture, but is easily lacerable by mechan- 

 ical force. If a vertical section of the 



kidney be made from its convex to its 



concave border, and the loose tissue and 



fat removed from around the vessels and 



the excretory duct, it will be seen that the organ consists of a central cavity surrounded, except 



at the hilum, by the proper kidney substance (Fig. 1094). This central cavity is called the 



renal sinus (sinus renalis) and is 

 lined by a prolongation of the cap- 

 sule, which is continued around 

 the lips of the hilum. Through 

 the hilum -the bloodvessels of the 

 kidney and its excretory duct pass, 

 and therefore these structures, upon 

 entering the kidney, are contained 

 within the sinus. 



The excretory duct or ureter 

 begins as a funnel-shaped sac, the 

 pelvis of the ureter (pelvis ureter- 

 icus s. renalis). The pelvis begins 

 at the renal papillae in the form of 

 a number of truncated cup-shaped 

 infundibular divisions, the calices 

 minores, into each of which usually 

 one papilla projects. These minor 

 calices vary from ten to twenty in 

 number. Several minor calices 

 unite to form larger divisions, the 

 calices majores (Fig. 1096), which 

 are usually two in number, though 

 more may be present. These 

 major calices unite to form the 

 main compartment of the pelvis, 

 which becomes narrowed below at 

 the level of the second lumbar ver- 

 tebra to be continued as the ureter 

 proper (Fig. 1096). 



The kidney substance or paren- 

 chyma consists of very irregular 

 tubules, the uriniferous tubules, 



elvis exposed, viewed whjch ^ ?upported by a fl?me _ 



work of retiform connective tissue 

 and surrounded by blood- and lymph vessels and nerves. It is readily divisible into an outer 

 third, the cortex, about one-third to one-half of an inch (8 to 12 mm.) in thickness, and an inner 

 two-thirds, the medulla, two-thirds to three-quarters of an inch (16 to 20 mm.) in thickness. 



CUT SURFACE 

 OF KIDNEY 



INFERIOR 

 EXTREMITY 



FIG. 1096. The right kidney with its 

 behind. 



