THE KIDNEYS 



559 



Examination with a pocket lens shows that the cortex is imperfectly divided 

 into lobules (Lobuli corticales). Each lobule consists of an axial radiate part (Pars 

 radiata), surrounded by a convoluted part (Pars convoluta). The former appear 

 as ray-like prolongations from the bases of the pyramids (hence also termed medul- 

 lary rays), and consist largely of narrow, straight or slightly flexuous tubules (limbs 

 of the loops of Henle). The convoluted part is granular in appearance, and con- 

 sists largely of the renal corpuscles and convoluted tubules. 



_ The renal pelvis (Pelvis renalis) is the dilated origin of the excretory duct. 

 It lies in the sinus of the kidney, and it is funnel-shaped, but flattened dorso-ven- 

 trally. The renal crest^ (Crista renalis) projects into the outer part of the pelvis 

 in the form of a horizontal ridge with a concave free edge. The tubules of the 

 middle part of the medullary substance open on this crest into the pelvis. The 

 tubules from each end of the kidney do not open into the pelvis proper (Recessus 

 medius), but into two long, narrow diverticula (Recessus terminales), which pro- 

 ceed from it toward the poles of the kidney. The wall of the pelvis consists of 

 three layers. The external fibrous coat or adventitia is continuous with the sup- 

 porting tissue of the kidney. The muscular coat consists of longitudinal and 



Fig. 500. — Cast of Right Renal Pelvis (a), Re- 

 cesses (c, cO, AND Origin of Ureter (6) 'of Horse. 

 (After Dumont.) 



Fig. 501. — Cast of Left Renal Pelvis (a), Recesses 

 (c, c'), AND Origin of Ureter (6) of Horse. 

 (After Dumont.) 



circular fibers. The mucous coat does not cover the renal crest nor is it continued 

 into the diverticula of the pelvis. It has a yellowish tinge, and forms numerous 

 folds. It contains compound tubular glands (Glandulse pelvis renalis), which 

 secrete the thick, viscid mucus always found in the pelvis.^ 



Renal Tubules. — The parenchyma or proper substance of the kidney is composed of the 

 small renal or uriniferous tubules (Tubuli renales), which are very close together and have a 

 complicated com-se. Each tubule begins in a thin-walled, spherical dilatation or capsule (Cap- 

 sula glomeruli), which is invaginated to receive a tuft of looped capillaries termed a glomerulus; 

 these two structures constitute a renal corpuscle; the corpuscles are visible as minute red or 

 dark spots in the convoluted part of the cortex. Succeeding this is a short narrow neck, beyond 

 which the tubule becomes wide and convoluted, forming the proximal convoluted tubule, and 

 enters the radiate portion of the cortex. It then gradually narrows and enters the intermediate ■ 

 zone; becoming very narrow and nearly straight, it descends for a variable distance into the medul- 

 lary substance, turns sharply upon itself, and returns to the cortex, forming thus the loop of Henle, 

 with its descending and ascending limbs. In the convoluted part of the cortex it widens and 

 becomes tortuous, constituting the distal convoluted tubule. The tubule then narrows, enters a 

 medullary ray, and opens with other tubules into a straight collecting tubule; this passes axially 

 through a pyramid, and unites with other collecting tubules to form the relatively large papillary 

 ducts, which open into the renal pelvis. 



Stroma. — The interstitial tissue forms a reticulum throughout which supports the tubules 



1 The crest is the result of fusion of the papillae or apices of the pyramids in the embryo and 

 is therefore also known as the papilla communis. 



^ There are goblet cells in the epithelium of the pelvis which doubtless concur in the secretion 

 of mucus. 



