THE KIDNEY 431 



On entering the glomerulus the artery divides into two vessels which 

 immediately subdivide with the formation of five hr.-niclies (Johnston). 

 Each of these branches forms a series of anastomosing capillary loops 

 whose convexity is directed away from the entering artery. The capillary 

 loops reunite, in a similar manner, to form the efferent vessel, which 

 leaves the glomerulus in company with the afferent; but, once out, they 

 soon part company, the efferent vessel breaking into a second capillary 

 plexus about the neighboring tubules. Within the glomerulus the capil- 

 laries are united by a very delicate but scanty connective tissue containing 

 no elastic fibers. 



The visceral layer of the capsule is firmly adherent to the walls of 

 the glomerular capillaries. It consists of a single layer of flat epithelial 

 cells which are intimately blended with each other and with the endothe- 

 lium of the capillaries. The epithelial cells possess a clear cytoplasm and 

 a flattened ovoid nucleus, which, being thicker than the body of the 

 cell, produces a considerable bulging. In fetal and infantile life the 

 shape of the cells of this layer is cuboidal or even low columnar, but 

 becomes more and more flattened as development progresses, until the 

 epithelium finally simulates a layer of endothelial cells. 



The epithelium of the parietal layer is also cuboidal in fetal life, 

 but during development becomes nearly as much flattened as that of the 

 visceral layer. Its single layer of finely granular cells forms a complete 

 lining for the capsule. It rests upon a homogeneous basement membrane 

 which is invested by a thin layer of connective tissue. This fibrous layer 

 is rather more highly developed about those renal corpuscles which lie 

 near the medulla than about those of the more peripheral portions of 

 the cortex. 



2. The Neck of the Tubule. In this portion of the tubule the 

 flattened epithelium of the glomerular capsule rapidly changes to the 

 low columnar type of the proximal convoluted portion. This section is 

 extremely short; it forms a constricted portion which marks the begin- 

 ning of the tortuous tubule. This constriction is more apparent than 

 real, since the caliber of the tubule in the neck is as great as in the 

 succeeding portion whose external diameter is, however, much increased 

 by the increasing height of the epithelial cells. This portion of the 

 tubule, being in relation with the renal corpuscle, is necessarily found 

 in the cortical labyrinth. 



3. The Proximal Convoluted Portion. This is commonly the 

 longest and broadest portion of the urinifcrous tubule. Collectively the 

 convoluted tubules form the greater part of the cortical labyrinth, in 



