EXCRETORY TUBES OF KIDNEY. 475 



the injected kidney red points (Maipighian bodies) are scattered amongst 

 the cortex, giving it a granular appearance. 



STRUCTURE OK THE KIDNEY. The mass of the kidney consists of 

 minute convoluted tubes, intermixed with bloodvessels, lymphatics, nerves, 

 and an intertubular matrix. The whole is incased by a fibrous coat. 



The fibrous coat is a white layer, which is connected with the kidney 

 by fine processes and vessels, but is readily detached from it by slight 

 force.- At the inner margin of the kidney it sinks into the sinus, and 

 sends processes on the entering vessels and excretory duct. 



Stroma or matrix. Between the tubules and the vessels of the kidney 

 is a uniting materal, which surrounds and isolates them, and is most abund- 

 ant in the cortical substance. It somewhat resembles areolar tissue in its 

 nature, and' is fibrous at some spots. 



To obtain a knowledge of the anatomy of the secreting tubes, and of the 

 bloodvessels, the dissector will require a microscope, and good fine injec- 

 tions of the kidney. 



Secretory tubules. The uriniferous tubes (tubuli uriniferi) occupy suc- 

 cessively the cortical substance, and the Maipighian pyramids ; but they 

 have a different arrangement in each part as below (fig. 164, a). 



In the Maipighian pyramid tubes are straight, and ascend from the 

 apertures in the apex, bifurcating repeatedly, as far as the base, and form- 

 ing a cone which resembles the stem and branches of a tree. At the wide 

 end of the pyramid they are collected into bundles which reach nearly to 

 the surface of the kidney, and become convoluted as they enter the cortex, 

 but some unite in arches (Henle). Near the apex they measure ^^th of 

 an inch across, but the last subdivisions are only half that size, or ^J^th 

 of an inch. 



Descending between the straight tubes are the small " looped tubes" of 

 Henle (fig. J 64, g). These run down from the cortical substance nearly 

 to the apex of the pyramid, where they turn upwards, forming loops with 

 the convexity down, and ascend to open into the straight tubes : their size 

 is about a third of the others. 



In the cortical substance the tubes are more numerous and very convo- 

 luted (fig. 165) ; they have an average width of (j^o tn ^ an inch, and are 

 surrounded by a capillary plexus of bloodvessels (fig. 166, A). At the 

 one end (farther) each tube is dilated into the Maipighian corpuscle (b) ; 

 and at the other it passes into a straight tube or joins an " arch" at the 

 base of the pyramid. The " looped tubes" of Henle (fig. 164) have the 

 same arrangement as the larger tubuli uriniferi in the cortical substance. 



The wall of the convoluted tubes consists of a thin basement membrane, 

 and is lined by a thick, nucleated, and granular epithelium. 



Maipighian corpuscles (fig. 166, A). These small bodies are connected 

 with the free ends of the convoluted tubes, one to each : and are arranged 

 in double rows in the cortical substance between the pyramids, one row 

 being on each side of an interpyramidal branch of artery, from which they 

 receive twigs ; each measures about T ^th of an inch, and consists of an 

 incasing capsule with an inclosed tuft of bloodvessels (glomerulus). 



The capsule (b) is the dilated end of the convoluted tube, and is per- 

 forated at the extremity by two small bloodvessels. Its wall consists of 

 a thin basement membrane, and is lined by a transparent laminar epithe- 

 lium. 



The glomerulus (fig. 166, B) is formed by the intercommunications 

 of two vessels piercing the capsule, and is clothed with epithelium. One 



