390 



BLOOD-VESSELS OF THE CORTEX. 



tubule, and is lined by similar cells. The curved collecting, or junctional tubule, although 

 narrow, has a relatively wide lumen, as it is lined by clear, somewhat flattened cells. 



The 'collecting tubes have a distinct lumen, and are lined by clear, somewhat irregular, 

 cubical cells (fig. 244, V), which in the larger excretory tubes are distinctly columnar (VI). 

 The basement-membrane is said to be absent in the larger tubes. [Klein describes a thin, 

 delicate, nucleated centro-tubular membrane lining the surface of the epithelium next the 



II. The Blood-Vessels. The renal artery (fig. 250) divides into four or five branches, which 

 pass' into the kidney at the hilum. These branches, surrounded by connective-tissue 

 continuous with that of the capsule, continue to divide, and pass between the papilla*, to reach 

 the bases of the pyramids on the limits between the cortical and boundary zones, where they 

 form incomplete arches. From these horizontal trunks, the interlobular arteries (fig. 243, 



,- 1 -^ a) run vertically and singly into 



jgl^ the cortex, between each two 



medullary rays, and in their 

 course they give off" on all sides 

 the short undivided vasa affer- 

 entia (1), each of which enters 

 a Malpighian capsule at the 

 opposite pole from which the 

 urinary tubule is given off. 

 Within the capsule, each afferent 

 artery breaks up into capillaries 

 arranged in lobules and sup- 

 ported by connective-tissue, the 

 whole forming a tuft of capillary 

 blood-vessels, or a glomerulus. 

 Each glomerulus is covered on 

 its surface, directed towards the 

 wall of the capsule by a layer of 

 flat, nucleated, epithelial cells 

 (fig. 229, II), which also dip 

 down between the capillaries. 

 A vein, the vas efferens (2), 



S3 



Fig. 244. 

 II, Bowman's capsule and glomerulus. 



a, vas afferens ; e, vas 



efferens; c, capillary network of the cortex ;*, endothelium wn ich is always smaller than the 



afferent arteriole, proceeds from 

 the centre of the glomerulus, 



of the capsule ; h, origin of a convoluted tubule. Ill, 



"rodded" cells from a convoluted tubule 2, seen from 



the side, with g inner ; granular zone; 1 from the surface. ;^ \ the capsule close to 



I\, cell lining Henles looped tubule. V cells of a col- the point at which the afferent 



lecting tube. VI, section of an excretory tube. vesg ^ enters it (fig ^ H) 



In their structure and distribution all the efferent vessels resemble arteries, as they divide into 

 branches to form a dense, narrow-meshed, capillary network (fig. 243, A, and fig. 244, II, c), 

 which ramifies over and between the convoluted tubules. The meshes are elongated around 



Fig. 245. 



Convoluted tubule (after ammonium chromate) 



showing "rodded" epithelium. 



Fig. 246. 



Epithelium of an irregular tubule 



of the kidney of a dog. 



the tubules of the medullary rays, and more polygonal around the convoluted tubules (fig. 243). 

 Some of the lowest efferent vessels split up into vasa recta, which run towards the medulla. 

 The interlobular arteries l>ecome smaller as they pass towards the surface of the kidney, and 

 some of their terminal capillaries communicate with the capillaries of the external capsule itself. 

 Venous trunks proceed from the capillary network, to terminate in the interlobular veins (V), 

 which begin close under the capsule by venous radicles arranged in a stellate manner (consti- 

 tuting the stellulse Verheynii, or venae stellatsa), and accompany the corresponding artery to 

 the limit between the cortex and boundary zone, where they communicate with the large venous 

 trunks in that situation. 



The blood-vessels of the medulla arise from the vasa recta (fig. 243, r), which begin on 

 the limit of the cortex and medulla, either as single, direct, muscular branches (r) of the large 



