BENAL PELVIS AND UEETEES 



447 



large plate-like cells of the superficial layer. The thin transitional epi- 

 thelium of the calyces is continuous with the columnar epithelium- o the 

 papillary ducts. 



The tunica propria, continuous with the renal interstitial tissue, 

 contains both col- 

 lagenous fibers 

 and elastic fibers. 

 1 1 is indistinctly 

 divisible into a 

 superficial denser 

 portion, and an 

 open-meshed deep 

 portion whose fi- 

 brous bands loose- 

 ly attach the mu- 

 cous membrane to 

 the muscular coat. 

 This deep layer is 

 analogous to t h e 

 submucosa of the 

 alimentary tract. 

 The mucous mem- 

 brane is thrown 

 into numerous 

 deep folds or rugae 

 which in the ure- 

 ter have a longi- 

 tudinal direction; 

 this condition 

 gives to the canal 

 in transverse sec- 

 tion a stellate ap- 

 pearance. Irregu- 

 lar folds or inva- 

 ginations of the 

 epithelium occur 

 in the renal pelvis 



and have been described as glands, but true secreting glands are not 

 found. Occasional lymphocytes occur in the mucosa, and small lymph 

 nodules have also been found but cannot be regarded as of constant 



FIG. 412. TRANSITIONAL EPITHELIUM OF DOG'S URETER. 



A, in the contracted condition; B, in the distended con- 

 dition; a, basal layer of cubic cells; 6, middle layer of polyg- 

 onal cells; c, superficial layer of rectangular and ovoid 

 cells. (R. W. Harvey, Anat. Rec., 3, 5, 1909.) X 750. 



