THE URINARY SYSTEM 327 



close proximity to the jMalpighian body from which it started, lying, 

 however, on the side of the afferent and efferent blood-vessels, i.e., on 

 the side opposite its point of origin. The second convoluted tubule 

 passes into the arched tubule (AC) which enters a medullary ray and 

 continues straight down through the medullary ray and medulla as 

 the straight or collecting tubule (SC). During its course the col- 

 lecting tubule receives other arched tubules. As it descends it be- 

 comes broader, enters the papilla, where it is known as the duct of 

 Bellini (ED), and opens on the surface of the papilla into the kid- 

 ney pelvis. About twenty ducts of Bellini open upon the surface of 

 each papilla, their openings being known as the foramina papillaria. 



Fig. 225. — Malpighian Body from Human Kidney. X280. (Technic 2, p. 331.) a, 

 Bowman's capsule; b, neck'; c, first convoluted tubule; d, afferent and efferent vessels. 



Each tubule consists of a delicate homogeneous membrana propria 

 upon which rests a single layer of epithelial cells. The shape and 

 structure of the epithelium differ in different portions of the tubule. 

 I. The Malpighian body is spheroidal, and has a diameter of from 

 120 to 2oo/«. The structure of the Malpighian body can be best 

 understood by reference to its development (Fig. 224). During the 

 ^' velopment of the uriniferous tubules and of the blood-vessels of the 

 .dney, the growing end of a vessel meets the growing end of a tubule 

 m such a way that there is an invagination of the tubule by the blood- 

 vessel (see Fig. 224). The result is that the end of the vessel which 

 develops a tuft-like network of capillaries — -the glomerulus — comes to 

 lie within the expanded end of the tubule, which thus forms a two- 

 layered capsule for the glomerulus. One layer of the capsule closely 

 invests the tuft of capillaries, dipping down into it and separating the 



