THE KIDNEYS 



1353 



emerges from the capsule at the same point. The afferent vessel is usually the larger of the two 

 (Fig. 1097). The Malpighian or Bowman's capsule, which surrounds the glomerulus, is formed 

 of a hyaline membrane, supported by a small amount of connective tissue, which is continuous 

 with the connective tissue of the tube. It is lined on its inner surface by a layer of squamous 

 epithelial cells, which are reflected from the lining membrane to the glomerulus, at the point of 

 entrance or exit of the afferent and efferent vessels. The whole surface of the glomerulus is 

 covered with a continuous layer of the same cells, which rests on a delicate supporting membrane 

 (Fig. 1097). Thus, beween the glomerulus and the capsule a space is left, forming a cavity lined 

 by a continuous layer of squamous cells; this cavity varies in size according to the state of 

 secretion and the amount of fluid present in it. In the fetufe and young subject the cells are 

 polyhedral or even columnar. 



At the junction of a tubule with the Malpighian capsule there is a somewhat constricted por- 

 tion, which is termed the neck (Fig. 1099). Beyond this the tubule becomes convoluted, and 

 pursues a considerable course in the cortical structure, constituting the proximal or first convo- 

 luted tubule (Figs. 1099 and 1102). After a time the convolutions disappear, and the tubule 

 approaches the medullary portion of the kidney in a more or less spiral manner. This section 

 of the tubule has been called the spiral tube of Schachowa. Throughout this portion of 

 their course the tubuli uriniferi are contained entirely in the cortical structure, and present a 

 fairly uniform calibre. They now enter the medullary portion, suddenly become much smaller, 



CAPSULE- 



LABYRINTH 

 OF CORTEX 



MEDULLARY 

 RAYS 



INTERLOBULAR 

 VEIN 



ft, CONVOLUTED 



""'TUBULES 



MALPIGHIAN 

 ORPUSCLES 



INTERLOBULAR 

 :), --'"ARTERY 



: 4 STRAIGHT 



' TUBULES 



FIG. 1098.- Part of a section through the cortex of the kidney in the direction of the straight tubules. (Toldt.) 



quite straight in direction, and dip down for a variable depth into the pyramids, constituting the 

 descending limb of Henle's loop. Bending on themselves, they form what is termed the loop of 

 Henle, and re-ascending, they become suddenly enlarged and again spiral in direction, forming the 

 ascending limb of Henle's loop, and reenter the cortical structure. In the cortex the tubule 

 again becomes slightly convoluted, and is called the distal or second convoluted tubule (Fig. 

 1099). This terminates in a narrow arched collecting or junctional tubuie, which enters the 

 straight collecting tubule. 



Each straight collecting tubule (tubulus renalis recta) passes from the cortex into the medulla, 

 receiving at various intervals in the cortical part of its course several arched collecting tubules. 

 In the medullary pyramid, several straight collecting tubules unite to form from sixteen to 

 twenty papillary or excretory ducts, which empty at the area cribrosa of the renal papilla. As 

 they approach the papilla, their diameter gradually increases. 



It will be seen from the above description that there is a continous series of tubes from their 

 commencement in the Malpighian bodies to their termination at the orifices on the apices of 

 the pyramids of Malpighi, and that the urine, the excretion of which commences in Bowman's 

 capsule, finds its way through these tubes into the calices of the ureter. 



Structure of the Uriniferous Tubule. The uriniferous tubule consists throughout of 

 a single layer of epithelial cells resting upon a basement membrane which is supported by a 

 delicate meshwork of retiform connective tissue. The tissue contains the vessels, nerves, and 



