1356 



THE URINOGENITAL ORGANS 



FIG. 1103. Lobar circulation. 



FIG. 1104. Interlobar circu- 

 lation. 

 (Poirier and Charpy.) 



which divides into anterior, middle, and posterior branches, which do not anastomose with each 

 other. The branches of the renal arteries pass to the kidney substance between the pyramids 

 and are known as interlobar arteries (arteriae interlobares renis) (Figs. 1098 and 1104). At the 

 junction of the cortical and medullary portions (the boundary zone) these vessels turn and for a 

 short distance pursue a course parallel to the kidney surface. There are thus formed a series of 

 incomplete vascular arches across the bases of the pyramids, the arcuate arteries (arteriae arci- 

 formes) (Figs. 1094 and 1 102). From these arches two sets of vessels come. The vessels of one set 

 go to the periphery and enter the cortex, the intralobular arteries, those of the other set pass 



toward the sinus and enter the medulla. 

 These last vessels are the arteriolae 

 recti (Figs. 1098 and 1102). As the 

 intralobular arteries pass toward the 

 capsule they give off branches to each 

 renal corpuscle, the vasa afferentia or 

 afferent arterioles. As the arteriole 

 enters the corpuscle it divides into 

 several branches, each of which forms 

 a capillary plexus. The blood from 

 each plexus is collected by a small 

 branch which joins with its fellows to 

 form the vas efferens or efferent 

 arteriole. These various plexuses 

 constitute a glomemlus or Malpighian 

 Tuft (Fig. 1097). On leaving the 

 glomerulus the arteriole forms a capil- 

 lary network around the adjacent 

 portions of the uriniferous tubule. 

 The blood is collected by various channels and emptied into the intralobular vein, which 

 starts in the venae stellatae, beneath the capsule, and empties its blood into the arcuate vein. 

 The arteriolae rectae supply the medulla and are smaller in diameter than the intralobular 

 arteries, and soon form a rich capillary plexus around the tubules of the medulla. The blood is 

 collected by the venae rectae, which empty into the arcuate vein (vena arciformis) at the boun- 

 dary zone. The blood is carried to the columns of Bertin, where it continues toward the sinus 

 in the interlobular veins. In the sinus these veins unite to form the renal vein (vena renalis) 

 (Fig. 1088). 



The nerves of the kidney, although small, are about fifteen in number. They have small 

 ganglia developed upon them, and are derived from the renal plexus, which is formed by branches 

 from the solar plexus, the lower and outer part of the semilunar 

 ganglion and aortic plexus, and from the lesser and smallest 

 splanchnic nerves. They communicate with the spermatic 

 plexus, a circumstance which may explain the occurrence of pain 

 in the testicle in affections of the kidney. So far as they have 

 been traced, they seem to accompany the renal artery and its 

 branches, and they have been traced to the epithelium, but their 

 exact mode of termination is not known. 

 The Lymphatics are described on page 799. 

 Variations and Abnormalities. Congenital absence of the 

 kidney has been observed. Not unusually one kidney is con- 

 siderably larger than the other; occasionally one is very large 

 and the other is very small, from atrophy, the large organ having 

 become large in response to a functional need, which causes it to 

 compensate for the insufficiency of the small kidney. If a kidney 

 is removed surgically, the other kidney enlarges. As previously 

 stated, the kidneys of the fetus and of the young child show 

 distinct fissures which make each organ lobulated (Fig. 1105). 

 The adult kidneys frequently exhibit remains of these fissures. 

 A horseshoe kidney is a condition in which the lower extremi- 

 ties of the two kidneys are united by kidney structure, the bond 

 of union crossing the middle line. The strip of kidney tissue which effects the junction may be 

 slight, considerable, or extensive in amount. Sometimes the two kidneys are completely fused 

 together into one large organ with two ureters. 



Surface Form. The kidneys, being situated at the back part of the abdominal cavity and 

 deeply situated, cannot be felt unless enlarged or misplaced. They are situated on the confines 

 of the epigastric and umbilical regions internally, with the hypochondriac and lumbar regions 

 externally. The left is somewhat higher than the right. According to Morris, the position of 

 the kidney may be thus defined: Anteriorly: "(1) A horizontal line through the umbilicus is 



FIG. 1105. Fetal kidney, showing 

 lobulation. (Testut.) 



