STRUCTURE OF THE KIDNEY. 471 



the side of the afferent vessel and in structure and further course resembles a 

 small artery. Throughout the entire cortex all of the efferent vessels enter into 

 the formation of a line capillary network (A and II, c), which surrounds the 

 urinary tubules. Within the range of the medullary rays of the cortex the fibers 

 of the network, in accordance with the straight course of the urinary tubules, are 

 arranged rather longitudinally, while in the remainder of the cortex their ar- 

 rangement is polygonal. From this capillary network of the cortex venous 

 radicles arise to form the interlobular veins (v). These originate just beneath 

 the fibrous capsule of the kidney from the union of the radicles of the smallest 

 venules arranged in a stellate manner (stellulae Verheynii or stellate veins) and 

 then pass each in the company of an interlobular artery to the junction of the 

 medulla and the cortex. 



The vessels of the medullary structure arise from the straight arterioles. These 

 either begin at the junction of the cortical and the medullary structure of the 

 kidney as individual, direct branches (r) of the interlobular arteVies, still provided 

 with muscular fibers, or they are formed from those efferent vessels (e) that lie 

 adjacent to the medullary structure of the kidney. The latter are said to be un- 

 provided with muscular fibers. Finally it is stated that a number of these vessels 

 are formed from the union of the capillaries of the medullary rays. All of the 

 straight arterioles, accompanying the straight urinary tubules, pass into elongated 

 brush-like capillary bundles, which surround the urinary tubules. From these 

 capillaries there collect throughout the entire extent of the medulla loops curving 

 upward and downward, representing the beginning of the veins. The latter pass 

 back toward the junction between the medullary and the cortical structure and 

 gradually constitute the straight venules (c), which empty into the lower portion 

 of the interlobular veins. On the papillae the capillaries of the medulla communi- 

 cate with vascular branches in garland-like arrangement surrounding the papil- 

 lary ducts. 



The vessels of the fibrous capsule of the kidney are derived in part from pene- 

 trating branches arising from the extremity of the interlobular arteries and in 

 part from branches of the suprarenal, phrenic and lumbar arteries, between which 

 anastomoses take place. The capillary network is a simple mesh-arrangement. 

 The venous radicles pass over in part into the stellate veins and in part into veins 

 of the same name as the arteries. A number of venous radicles also pass out of 

 the cortex. The communication between the distribution of the renal artery and 

 other arteries in the capsule explains the fact that after ligation of the renal 

 artery within the kidney the blood-stream may enter from the capsule. Arterial 

 blood also is sent to the kidney and this may even give rise to a slight secretion. 



Lymphatics are present within the fibrous capsule as a wide-meshed 

 network and beneath the capsule in the form of spaces of considerable size. 

 In the parenchyma of the kidney itself the lymph is said to circulate between 

 the urinary tubules and the blood-vessels, in tissue-spaces without walls which 

 are found in larger number around the convoluted tubules than around the 

 straight tubules. The spaces reach to the surface of the kidney and are dis- 

 tributed extensively beneath the capsule. Marked distention of the lymph-spaces 

 compresses the urinary tubules and the vessels. Large lymphatics, provided 

 with valves, are visible at the hilus of the kidney, while others pass through 

 the fibrous capsule, both communicating with the lymph-spaces of the capsule 

 of the kidney. 



Of the nerves, branches provided with ganglia accompany the afferent vessels. 

 Non-medullated fibers penetrate to the surface of the capsule and between the 

 urinary tubules. It is established physiologically that motor fibers are present 

 for the unstriated muscular fibers, also vasomotor fibers and sensory branches in 

 the capsule and the pelvis of the kidney. The existence of vasodilator and 

 secretory fibers is also probable. 



The connective tissue of the kidney forms in the papillae fibrillated, con- 

 centric layers about the excretory ducts (VI). Further upward star-shaped cells 

 of reticular tissue appear in addition and these are found alone in the cortex. 

 The outer layers of the fibrous capsule of the kidney are formed of dense bundles 

 of fibrils, while the inner layers are looser and send processes into the cortical 

 layer. The fatty capsule of the kidney is connected with the organ itself, in part 

 through vessels and in part through bands of connective tissue. 



Unstriated muscular fibers are contained in the kidney in three forms: (i) 

 A sphincter-like layer surrounding each papilla; (2) a wide-meshed net- 

 work on the surface of the kidney; (3) fibers that arise from the depth of the 

 pelvis of the kidney and pass through the pyramids with the blood-vessels 



