THE URINARY ORGANS. 



201 



THE RENAL SINUS AND THE URETER. 



The greater part of the renal sinus is occupied by the dilated, 

 pouch-like expansion of the upper extremity of the excretory duct 

 of the kidney, the ureter, embracing the pelvis and its subdivisions, 

 the calices, and the infundibula. These cavities, together with the 

 protruding portions of the renal papillae, are invested by a membra- 

 nous structure consisting of three coats, the mucous, the muscu- 

 lar, and the fibrous. The mucous coat is covered with stratified 

 squamous epithelium, which comprises relatively few layers of cells, 

 and is frequently termed ' ' transitional, ' ' in view of the rapid change 



FIG. 244. 



Transverse section of human ureter : a, irregular lumen, lined by mucous membrane, which con- 

 sists of epithelium (b), tunica propria (c),and submucous tissue (e/)', e,f, longitudinal and circular 

 bundles of muscular tunic ; g, additional longitudinal muscular bundles ; h, fibrous tissue ; /, blood- 

 vessels. 



from the columnar elements of the deep layer to the squamous ones 

 of the superficial stratum. The tunica propria, or stroma of the 

 mucous membrane, consists of a felt-work of fibro-elastic bundles, 

 contains a few small racemose glands, and passes insensibly into 

 the inconspicuous submucous tissue. The muscular coat is 

 arranged as an inner longitudinal and an outer circular layer 

 composed of bundles of involuntary muscle cells. On the papillae 

 the circular bundles are especially well developed, enclosing the renal 

 tissue somewhat as a sphincter. The outer fibrous coat consists of 

 irregularly-placed bundles of connective tissue, which connect the 

 organ with the surrounding structures. The walls of the ureter 



