THE FEMALE GENITAL ORGANS. 



359 



the vagina. They are relatively simple in structure, form irregular 

 tubes, and are lined by ciliated columnar epithelium. The excre- 

 tory ducts are lined by stratified squamous epithelium. Diffuse 

 adenoid tissue is met with in the mucosa, which sometimes assumes 

 the form of lymphatic nodules. 



The muscular coat, which in the lower region is quite prominent, 

 may be separated indistinctly into an outer longitudinal and an in- 

 ner circular layer ; the latter is, as a rule, poorly developed, and may 

 be entirely absent. The muscular coat is especially well developed 

 anteriorly in the neighborhood of the bladder. 



Fig. 287. From section of human labia minora. 



The outer fibrous layer consists of dense connective tissue 

 loosely connected with the adjacent structures. 



At its lower end the vagina is partially closed by the hymen 

 which must be regarded as a rudiment of the membrane which in 

 the embryo separates the lower segment of the united Miillerian 

 ducts from the ectoderm of the sinus urogenitalis. Accordingly, 

 the epithelium on the inner surface of the hymen partakes of the 

 character of the vaginal epithelium ; that on the outer surface re- 

 sembling the skin in structure (G. Klein). 



