THE OVIDUCTS 225 



months an o\'inn is norniallydiscliarged from the o\ary and, pro\idcd 

 no sperm are present in the oviduct to fertihze the ovum, the special 

 l)reparation of tlie mucosa is not needed. A consequent loss of the 

 major ])ortion of the nnicosa takes place under the name of menstrua- 

 tion in humans, but in other forms degeneration and resorption 

 takes place in such cases. Following fertilization, more profound 

 changes occur in the body of the uterus if the embryo continues to 

 develop, so a description of the histological structures of the uterus 

 must also indicate the relation to ovidation and pregnancy. At 

 certain periods of the lunar month in humans, and at other inter- 

 cyclic periods for other animals, there is a condition which may be 

 described as the resting condition of the uterus. The lining of 

 such a uterus shows longitudinal ridges, due to the folding of the 

 tunica propria beneath the superficial layer of ciliated columnar 

 cells. Also in the mucosa are tubular glands extending more or 

 less perpendicularly toward the myometrium. Some of the colum- 

 nar cells forming these glands are also ciliated. Just beneath the 

 superficial epithelium of the lumen and surrounding the gland cells 

 is a rich reticular network with many mesenchyme-like cells and 

 leukocytes (especially lymphocytes). In the underlying tunica 

 I)ropria there is a rich capillary network derived from the vessels 

 in the myometriimi. At its posterior extremity the uterus narrows 

 to a short neck-like portion, the cervix, which joins the \'agina. In 

 this region the mucosa has only the superficial co^'ering of columnar 

 epithelium without any glands. The changes that occur in the 

 uterus preliminary to and following menstruation and ])regnancy 

 will be considered separately imder those headings. 



The Vcujina. This, is a tube-like portion continuous with the 

 uterus and receives the copulatory organ, the penis, of the male. 

 The same three coats are present in it as in the anterior portion of 

 the ducts, an adventitia, a muscularis, and a mucosa. The adven- 

 titia is similar to that of the uterus and Fallopian tubes. The 

 muscularis is much thinner than that of the uterus, with an ex- 

 ternal longitudinal and an internal circular region of muscle tissue. 

 At the lower end of the vagina the muscularis forms a sphincter 

 muscle. The mucosa consists of a coat of stratified squamous 

 epithelium lining the lumen and a subjacent vascular region of 

 connective tissue, the tunica propria, or corium, which may have 

 projecting papilki- that throw the epithelium into ridges. Three 

 zones are distinguishable in the epithelial lining: the one adjacent 

 15 



