274 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



At the urethral opening the middle layer is thickened 

 to form a sphincter muscle, according to some au- 

 thors. The bladder musculature forms a basket- 

 work fabric, and when much distended intervals 

 may arise in its walls which become points of weak- 

 ness through which the mucosa may protrude, when 

 the organ is said to be sacculated. 



Vessels and Nerves. The bladder is supplied with 

 blood from the superior and inferior vesicle arteries, 

 and in the female also from branches of the uterine 

 artery. The veins form large plexuses, particularly 

 around the neck, sides and base. They eventually 

 drain into the internal iliac. The nerve supply is 

 from the third, fourth, and sometimes the second 

 sacral nerves, and from the hypogastric plexus of the 

 sympathetic The latter are nearly all non-medul- 

 lated. 



