THE DEVELOPMENT OF THE UROGENITAL SYSTEM. 419 



THE UTERUS AND VAGINA. The fused caudal ends of the two Miillerian 

 ducts form the anlage of the uterus and vagina, which is a single medial tube 

 opening into the urogenital sinus (Fig. 363). During the third month certain 

 histological changes bring about a differentiation between the cephalic end or 

 uterus and the caudal end or vagina. The simple columnar epithelium of the 

 vaginal portion changes to stratified squamous, and during the fourth month 

 the lumen becomes closed. Near the external orifice a semicircular fold ap- 

 pears, which represents the hymen (Fig. 372). During the sixth month the 

 lumen reappears by a breaking down of the central ceils. The epithelium of 

 the uterus, primarily high columnar, becomes lower and toward the end of 

 fetal life acquires cilia. Many irregular folds appear in the mucosa of the 

 vagina, a smaller number in the uterus (Fig. 372). Some of the folds in the 



g Ovary 



Mesovarium 



Broad ligament 

 with paroophoron 



Oviduct 



Mesosalpinx 

 with epoophoron 



FIG. 373. Transverse section through the ovary and broad ligament of a human 

 foetus of 3 months. Nagel. 



uterus constitute the regular plica palmata of the cervix. The uterine glands 

 represent evaginations from the epithelial lining. They do not begin to develop 

 until after birth (one to five years), and their development is usually not com- 

 pleted until the age of puberty. 



The muscle and connective tissue of the walls of the uterus and vagina are 

 derived from the mesenchyme which surrounds the Miillerian ducts. The 

 muscle develops relatively late (after the fourth month of fcetal life). 



ATROPHY OF THE MESONEPHROI. By far the greater part of each meso- 

 nephros degenerates and disappears, and the parts that do persist are rudimentary 

 and possess no functional significance. The cephalic portion leaves ten to 

 twenty coiled tubules which terminate blindly at one end and at the other end 

 open into a common duct that represents the cephalic end of the mesonephric 

 duct. These tubules constitute the epoophoron (parovarium, organ of Rosen- 



