1128 



THE URINARY ORGANS. 



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 smooth 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 remnant of the lobular construction of the gland. The kidney is dense 



in texture, but is easily lacerable by mechanical 

 force. In order to obtain 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 from around 

 the vessels and the excretory duct (Fig. 716). 

 It will be then seen that the kidney consists of 

 a central cavity surrounded at all parts but one 

 by the proper kidney-substance. This central 

 cavity is called the sinus, and is lined by a pro- 

 longation 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 

 by kidney-structure. Through this fissure the 

 blood-vessels of the kidney and its excretory 

 duct pass, and therefore these structures, upon 

 entering the kidney, are contained within the 

 sinus. The excretory duct, or ureter, after 

 entering, dilates into a wide, funnel-shaped sac 

 named the pelvis. This divides into two or three 

 tubular divisions, which subdivide into several 

 short, truncated branches named calices or in- 

 fundibula, all of which are contained in the 

 central cavity of the kidney. The blood-vessels 

 of the kidney, after passing through the hilum, 

 are contained in the sinus or central cavity, lying between its lining membrane 

 and the excretory apparatus, before entering the kidney-substance. 



This central cavity, as before mentioned, is surrounded on all sides except at 

 the hilum by the substance of the kidney, which is at once seen to consist of two 

 parts viz. of an external granular investing part, which is called the cortical 

 portion ; and of an internal part, the medullary portion, made up of a number of 

 dark-colored pyramidal masses, with their bases resting on the cortical part and 

 their apices converging toward the centre, where they form prominent papillae 

 which project into the interior of the calices. 



FIG. 716. Vertical section of kidney. 



