132 



BIOLOGY OF THE LABORATORY MOUSE 



adipose cells. The mucous membrane forms low longitudinal folds. The 

 ureters enter the dorsal wall of the neck of the bladder close to one another. 

 Bladder. — The bladder is lined by transitional epithelium consisting, 

 when the organ is empty, of about four to five layers of cells. The fibrous 

 lamina propria is rich in blood vessels. The mucous membrane is thrown 

 into wide irregular folds and occasionally contains an aggregation of lympho- 

 cytes. When the bladder is in a distended condition the folds are absent 

 and the epithelial lining is very thin. The smooth muscle coat consists of 



Epithelium 



Blood vessel 



Lamina propria 



Fig. 62. — Bladder. (X200.) 



irregular muscle bundles of varying size, separated from each other by 

 considerable amounts of connective tissue (Fig. 62). At the neck of the 

 bladder the direction of the muscle bundles is circular. 



Female urethra. — The female urethra is a dorsoventrally slightly flat- 

 tened tube which originates at the neck of the bladder and opens into the 

 clitoral fossa. Near its origin the tube is lined by transitional epithelium 

 which soon changes into stratified squamous type. The lamina propria is 

 formed by loose connective tissue. The mucous membrane forms longitu- 

 dinal folds. The epithelium forms invaginations which are continuous with 

 gland tubules of the urethral glands. These glands are similar in structure 

 to the urethral glands (of Littre) in the male. The circularly arranged 

 smooth muscle fibers forming the outer wall are well developed. Near the 



