928 



THE KIDNEYS. 



three distinct glandular masses have been found, the supernumerary organ being 

 placed either in front or on one side of the vertebral column, or in the pelvic cavity. 



Structure. The kidney is surrounded by a proper fibrous coat, which 

 forms a thin, smooth, but firm investment, closely covering the organ. It 

 consists of dense fibro-areolar tissue, together with numerous fine elastic 

 fibres, and can easily be torn off from the substance of the gland, to which 

 it adheres by minute processes of connective tissue and vessels. 



On splitting open the kidney by a longitudinal section, from its outer to 

 its inner border, the fissure named the hilus is found to extend some dis- 

 tance into the interior of the organ, forming a cavity called the sinus of the 

 kidney, into the bottom of which the fibrous coat is prolonged. In such 

 a section, also, the commencement of the excretory duct and the disposition 

 of the substance of the organ are seen to the greatest advantage. 



The ureter, or excretory duct of the gland, which is dilated at its upper 

 end as it approaches the hilus, is seen to expand within the sinus into a 

 funnel-shaped cavity, compressed from before backwards, named the pelvis of 

 the kidney. Within the sinus, partly concealed by the vessels, the pelvis 

 divides usually into three, or sometimes only two, principal tubes, which 

 subdivide into several smaller tubes named the calyces or infundibula. 

 These calyces, which vary in number from seven to thirteen or more, form 

 short funnel-shaped tubes, into each of which a papilla of the renal sub- 

 stance projects. A single calyx often surrounds two, sometimes even three 

 papillae, which are in that case united together : hence, the calyces are in 

 general not so numerous as the papillae. The spaces between the calyces are 

 occupied by a considerable amount of fat, imbedded in which are seen the 

 main branches of the renal vessels. 



Fig. 649. 



Fig. 649. PLAN OF A LONGITUDINAL SEC- 

 TION THROUGH THE PELVIS AND SUBSTANCE 



OF THE RIGHT KIDNEY. 



a, the cortical substance ; 5, 5, broad part 

 of two of the pyramids of Malpighi ; c, c, 

 the divisions of the pelvis named calyces, or 

 infundibula, laid open ; c', one of these un- 

 opened ; d, summit of the pyramids or pa- 

 pillae projecting into calyces ; e, e, section of 

 the narrow part of two pyramids near the 

 calyces ; p, pelvis or enlarged divisions of the 

 ureter within the kidney ; u t the ureter ; s, 

 the sinus ; h, the hilus. 



Like the rest of the ureter, the 

 pelvis and greater part of the calyces 

 consist of three coats, viz., a strong 

 external fibro-areolar and elastic tunic, 

 which becomes continuous round the 

 bases of the papillae with that part of 

 the proper coat of the kidney which 

 is continued into the sinus ; secondly, 



a thin internal mucous coat, which is reflected over the summit of each 

 papilla ; and thirdly, between these two, a double layer of muscular fibres, 

 longitudinal and circular. The longitudinal fibres are lost near the base of 

 the calyx, but the circular fibres, according to Henle, form a continuous 



