THE RENAL DUCTS. 



1897 



more or less blended, a distinct submucosa being wanting. The mucous membrane 

 is clothed with ' ' transitional ' ' epithelium consisting of several strata of cells, the su- 

 perficial elements being plate-like and the deepest ones irregularly columnar. The 

 tunica propria constitutes a subepithelial layer of fibro-elastic tissue which blends with 

 the subjacent muscular tunic. Within the ureter the mucous membrane is usually 

 thrown into longitudinal folds, and in consequence in transverse section the lumen 

 of the canal appears stellate. Neither well-marked papillae nor true glands are pres- 

 ent, although in places the subepithelial tissue invades the epithelium and subdivides 

 the latter into nest-like groups of cells. Occasional aggregations of lymphoid cells 

 occur, which in the vicinity of the calyces sometimes form distinct minute lymph- 

 nodules within the mucosa (Toldt). On the papillae the epithelium lining the renal 

 duct passes uninterrupted into that of the papillary canals, while the underlying tunica 

 propria becomes continuous with the intertubular renal stroma. The muscular tunic 

 consists of bundles of the involuntary variety disposed as a thin inner longitudinal 

 and a chief external circular layer. Within the renal pelvis and its larger subdivisions 

 both layers are well represented, but are reduced on the calyces ; at the junction of 

 the latter with the kidney the circular muscle increases and surrounds the papilla 

 with a minute sphincter-like bundle (Henle). Except in the upper part of the renal 



Epithelium 



Mucous coat, thrown 

 into longitudinal folds 



Inner longitudinal 

 muscular bundles 



Fibrous coat 



>t< f' ; Outer longitudinal 

 /<*;' muscular bundles 



Circular muscular bundles 



Transverse section of ureter. X 25. 



duct, an additional imperfect outer longitudinal layer of muscle is represented by 

 irregularly scattered bundles. The fibrous coat, or tunica adventitia, composed of 

 bundles of fibrous and elastic tissue, invests the renal duct as its outer tunic and con- 

 nects it with the surrounding areolar tissue. At the kidney the outer coat of the 

 renal duct blends with the tunica fibrosa that invests the renal substance between the 

 calyces. Beginning several centimetres above the bladder, the adventitia of the 

 ureter is strengthened and thickened by robust longitudinal bundles of involuntary 

 muscle that follow the duct to its vesical orifice and, in conjunction with the fibrous 

 tissue in which they are embedded, form the ureteral sheath (Waldeyer). Accord- 

 ing to Disse, this muscle belongs to the wall of the ureter and is distinct from the 

 musculature of the bladder. 



Vessels. The arteries supplying the different segments of the renal duct are 

 derived from several sources. Those distributed to the pelvis and the adjoining part 

 of the ureter are small branches from the renal artery, the abdominal portion of the 

 canal being additionally supplied by twigs given off from the spermatic (ovarian) artery 

 as the latter crosses the duct and by a special vessel (a. ureterica) proceeding from 

 the internal or common iliac artery or from the aorta (Krause). The pelvic portion 

 receives branches from the middle hemorrhoidal or the inferior vesical arteries. The 



