986 



THE URINARY ORGANS. 



and Transversalis muscles, one or two of the upper lumbar arteries, the last dorsal, 

 ilio-hypogastric, and ilio-inguinal nerves. The right kidney rests upon the twelfth 

 rib, the left usually on the eleventh and twelfth. The Diaphragm separates the 

 kidney from the pleura as it dips down to form the phrenico-costal sinus, but fre- 

 quently the muscular fibres of the Diaphragm are defective or absent over a trian- 

 gular area immediately above the external arcuate ligament, and when this is the 

 case the perirenal areolar tissue is in immediate apposition with the diaphragmatic 

 pleura. 



The external border is convex, and is directed outward and backward, toward 

 the postero-lateral wall of the abdomen. On the left side it is in contact, at its 

 upper part, with the spleen. 



The internal border is concave, and is directed forward and a little downward. 

 It presents a deep longitudinal fissure, bounded by a prominent overhanging ante- 

 rior and posterior lip. This fissure is named the hiltom, and allows of the passage 

 of the vessels, nerves, and ureter into and out of the kidney. 



The superior extremity, directly slightly inward as well as upward, is thick 

 and rounded, and is surmounted by the suprarenal capsule, which covers also a 

 small portion of the anterior surface. 



The inferior extremity, directed a little outward as well as downward, is 

 smaller and thinner than the superior. It extends to within two inches of the 

 crest of the ilium. 



At the hilum of the kidney the relative position of the main structures passing 

 into and out of the kidney is as follows : the vein is in front, the artery in the 

 middle, and the duct or ureter behind and toward the lower part. By a knowledge 

 of these relations the student may distinguish between the right and left kidney. 

 The kidney is to be laid on the table before the student on its posterior surface, 

 with its lower extremity toward the observer that is to say, with the ureter 



behind and below the other vessels ; the hilum 

 will then be directed to the side to which the 

 kidney belongs. 



General Structure of the Kidney. The kidney 

 is surrounded by a distinct investment of fibrous 

 tissue which forms a firm, smooth covering to the 

 organ. It closely invests it, but can be easily 

 stripped off, in doing which, however, numerous 

 fine processes of connective tissue and small blood- 

 vessels are torn through. Beneath this coat a 

 thin wide-meshed network of unstriped muscular 

 fibre forms an incomplete covering to the organ. 

 When the fibrous coat is stripped off, the surface 

 of the kidney is found to be f-mooth and even 

 and of a deep-red color. 



In infants fissures extending for some depth 

 may be seen on the surface of the organ, a rem- 

 nant of the lobular construction of the gland. 

 The kidney is dense in texture, but is easily 

 lacerable by mechanical force. In order to ob- 

 tain a knowledge of the structure of the gland, 

 a vertical section must be made from its convex 

 to its concave border, and the loose tissue and 

 fat removed around the vessels and the excretory 

 duct (Fig. 543). It will be then seen that the 

 kidney consists of a central cavity surrounded at 



rp all parts but one by the proper kidney-substance. 



Ihis central cavity is called the sinus, and is lined by a prolongation of the fibrous 

 coat of the kidney, which enters through a longitudinal fissure, the hilum (before 

 mentioned), which is situated at that part of the cavity which is not surrounded 





FIG. 543. Vertical section of kidney. 



