EXCRETION 



463 



duct (Fig. 202). This cavity is mainly occupied by the upper part of the 

 renal duct, the ureter, the interior of which is termed the pelvis. The ureter 

 divides into several portions which terminate in small caps or calyces which 

 receive the apices of the pyramids. The parenchyma of the kidney consists 

 of two portions, viz. : 



1. An internal or medullary portion, consisting of a series of pyramids^or 



cones, some twelve or fifteen in number, which present a distinctly 

 striated appearance. 



2. An external or cortical por- 2/ , 



tion, twelve millimeters in 



thickness and distinctly 



friable in character. 

 A histologic analysis of 

 the kidney shows that it is 

 composed of a connective- 

 tissue framework supporting 

 secreting tubules, blood-ves- 

 sels, lymphatics and nerves, 

 all of which are directly con- 

 nected with the removal of 

 the urinary constituents from 

 the blood. 



The Tubules of the Kid- 

 ney. From its structure it 

 is apparent that the kidney 

 is a compound tubular gland, 

 the orifices of exit being di- 

 rected toward the pelvis. If 

 the apex of each pyramid be 

 examined with a lens, it will 

 present a number of small 

 orifices which may be re- 

 garded as the terminations 



of the uriniferous tubules. Fm ^.-LONGITUDINAL SECTION THROUGH THE 

 Each tubule begins in the KIDNEY, THE PELVIS OF THE KIDNEY, AND A NUMBER OF 

 cortical portion as a dilated ENAL CALYCES. A. Branch of the renal artery U. 

 j i T Ureter. C. Renal calyx, i. Cortex, i'. Medullary 



invagmated capsule known rays> I // > Labyrinth, or cortex proper. 2. Medulla, 

 as M tiller's or Bowman's 2'. Papillary portion of medulla, or medulla proper. 



ransule which receives a 2 "' Border la y er of the medulla. 3, 3. Transverse sec- 

 ! wnicn recei s a ^ through the axes of the tubules of the border layer 



small tuft Of blood-vessels, 4 . Fat of the renal sinus. 5, 5. Arterial branches, 

 the glomerulus. Just be- . Transversely coursing medulla rays. (Tyson, after 



yond the capsule the tubule He e -> 



becomes constricted after which it becomes enlarged and pursues a tortu- 

 ous course in the cortex though gradually approaching the base of the 

 pyramid (Fig. 203). In this region the tubule narrows extremely and 

 passes toward the apex of the pyramid, forming the descending limb of the 

 loop of Henle, where it turns on itself and again passes toward and into the 

 cortex forming the ascending limb of the loop of Henle. On reaching the 

 cortex, the tubule again enlarges and pursues a tortuous course not unlike 

 that of the proximal portion. The tubule then enters at some level and in 



