EXCRETION 



459 



duct (Fig. 205). This cavity is mainly occupied by the upper part of the 

 1 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. r 



2. An external or cortical por- 



tion, half an inch 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 beginnings 

 of the uriniferous tubules. 

 From this point the tubules 



pass Olltward in a Straight but n Ureter . C. Renal calyx, i. Cortex, i'. Medullary 



Somewhat diverging manner ra ' y s. i"/ Labyrinth, or cortex proper. 2. Medulla. 



tnwarH tV.P rnrtpv aivinP" off 2'. Papillary portion of medulla, or medulla proper. 



toward tne COrteX, giving On ^i^ jy~ ^ ^ me dulla. 3, 3- Transverse sec- 



at aCUte angles a number Of tion throug h the axes of the tubules of the border layer. 

 branches (Fig. 206). From . Fat of the renal sinus 5 ,5- 



the apex to the base of the 

 pyramids they are known as 



the tubules of Bellini. In the cortical portion of the kidney the tubule be- 

 comes enlarged and twisted, and, after pursuing an extremely convoluted 



- 



FIG. 205. LONGITUDINAL SECTION THROUGH THE 



c ursmg meduUa rayS '~ 



course 



, turns backward into the medullary portion for some distance, form- 

 ing the ascending limb of Henle's loop; it then turns upon itself, forming 

 the descending limb of the loop, reenters the cortex, again expands and 

 comes convoluted, and finally terminates in an ovoid mvaginated en large- 

 ment known as Muller's or Bowman's capsule, which receives a small 

 of blood-vessels the glomerulus. Each tubule consists of a basement mem- 



