BLADDER. 



26l 



The tunica muscularis is not compact since there is considerable con- 

 nective tissue among its smooth muscle bundles. The latter form an inner 

 longitudinal and an outer circular layer. In the lower half of the ureter 

 there is a third, outer longitudinal layer. Around the papillae of the kid- 

 ney the circular fibers form a "sphincter." The part of the ureter which 

 passes obliquely through the wall of the bladder has only longitudinal fibers 

 ending in the tunica propria of the bladder. By contracting they open the 

 outlet of the ureter. The adventitia consists of loose fibro-elastic con- 

 nective tissue. 



Lymphatics and blood vessels are numerous. There are sympathetic 

 nerves to the muscles, and free sensory endings in the tunica propria and 

 epithelium. 



Pit. 



Tangential sections of pits. 

 / V 



Secretion. 



Gland. 



Tunica propria. Smooth muscles. 



FIG. 297. SECTION' THROUGH THE FUXDUS OP THE URINARY BLADDER OF AX ADULT MAX. X 48. 



BLADDER. 



The development of the bladder from the proximal end of the allan- 

 tois has been described on page 193. Since the allantois is a part of the 

 entodermal tract, the epithelium of the bladder is entodermal whereas 

 that of the ureter is mesodermal. There is however no demarcation 

 between the layers in the adult, since both produce the same sort of "tran- 

 sitional epithelium." 



The bladder consists of a mucosa, submucosa, muscularis and serosa. 



