328 THE ORGANS 



groups of capillaries (see p. 333). This layer by modification of the 

 original epithelium of the tubule is finally composed of a single layer 

 of flat epithelial cells with projecting nuclei. The outer layer of the 

 capsule lies against the delicate connective tissue which surrounds 

 the Malpighian body. This layer consists of a similar though slightly 

 higher epithelium and is known as Bowman's capsule. Between the 

 glomerular layer of the capsule and Bowman's capsule proper is a | 

 space which represents the beginning of the lumen of the uriniferous 

 tubule (Fig. 225), the epithelium of Bowman's capsule being directly 

 continuous with that of the neck of the tubule. 



B 



. ^^ ,-t3 ■ "^^ V '^';:....- • '-:,-•- 



-&= 



i"- ft- 



A 



Fig. 226. — Proximal Convoluted Tubules of Human Kidney. X35°- (Technic 2, 



P- 33^-) A, Cross-section; B, oblique section. 



2. The Neck. — This is short and narrow, and is lined by a few 

 cuboidal epithelial cells. Toward its glomerular end the epithelium 

 is transitional between the flat epithelium of Bowman's capsule and 

 the cuboidal epithelium of the neck proper. At its other end the 

 epitheHum of the neck becomes larger and more irregular as it passes 

 over into that lining the next division of the tubule (Fig. 225. c). 



3. The first convoluted tubule (Fig. 226) measures from 40 to 70," 

 in diameter. It is lined by irregularly cuboidal or pyramidal epithe- 

 lium, with very indistinct demarcation between the cells. The cyto- 

 plasm is granular, and the granules are arranged in rows, giving the 

 cell a striated appearance. This is especially marked at the basal 

 end of the cell where the nucleus is situated. A zone of fine striations 

 along the free surface fiequently presents somewhat the appearance 

 of cilia. 



4. The descending arm of Henle's loop is narrow (Fig. 227, i), 

 10 to i5/< in diameter. It is lined by a simple flat epithelium. The 



