.)//rA' o.sro/'/r ANATOMY OF THE ORGAXS. 



appear, and the epithelial sheath itself becomes thinner and the 

 cells flatter. The tunica propria consists of fine connective 

 tissue which contains leucocytes, and small collections of 

 lymphocytes which sometimes form solitary follicles. This 

 layer passes over gradually into the submucosa. Here glands 

 are wanting. In sections infoldings of the mucosa are some- 

 times cut across, and were formerly thought to be glands in the 

 submucosa. 



The muscularis consists of two layers of smooth muscle cells, 

 one longitudinal, and the other circular (Fig. 172). In the 

 lower third of the ureter there is outside the circular coat a 

 third layer, which consists of bundles of muscle fibres running 

 longitudinally. In the calyces of the kidney there is no longi- 

 tudinal muscle coat whatever ; the circular coat forms an annu- 

 lar muscle around the base of each papilla. 



In the urinary bladder of man we can distinguish three 

 layers of muscle, of which the inner and outer are longitudinal, 

 and the middle circular. These layers cannot be separated defi- 

 nitely, for there is a manifold anastomosis between the bundles 

 of the different layers. Two fixed points of the bladder give a 

 basis for the study of the musculature. These are the point at 

 which the urachus is attached, and the triangle formed by lines 

 drawn between the openings of the ureters and the urethra 

 i. e., the trigone. Remembering that the bladder is developed 

 from the inner third of the allantois, which is a more or less 

 tubular structure, these two points represent the two ends 

 of the tube. 



The fibrous sheath of the urinary tract consists of fine con- 

 nective tissue in which many blood-vessels and nerves are 

 found. 



The blood- and lymph-vessels form a capillary network in 

 the tunica propria. 



The nerves are spread out mainly in the muscle coat, with 

 a certain number of fibres reaching as far as the epithelium. 



