OVULATION AND MENSTRUATION 723 



and veins are found in large numbers in the outer part so as to form almost a 

 special vascular coat. The mucous membrane of the uterus is composed of 

 columnar ciliated epithelium, which extends also to the interior of the 

 tubular glands, of which the mucous membrane is largely made up. In the 

 cervix of the uterus the mucous membrane is arranged in permanent longi- 

 tudinal folds, plica palmatT. The glands of this part branch repeatedly, 

 and extend deeply into the substance of the cervix. The body has numerous 

 simpler tubular glands. The glands are also lined with ciliated epithelium. 

 They secrete a thick glairy mucus, resembling white of egg. 



The Vagina. The vagina is a membranous canal 8 to 10 cm. long, 

 extending obliquely downward and forward from the neck of the uterus, 

 which it embraces, to the external organ of generation. It is lined with 

 mucous membrane, covered with stratified squamous epithelium, which in 

 the ordinary contracted state of the canal is thrown into transverse folds. 

 External to the mucous membrane, the walls of the vagina are constructed 

 of unstriped muscle and fibrous tissue, within which in the submucosa, 

 especially around the lower part of the tube, is a layer of erectile tissue. The 

 lower extremity of the vagina is embraced by an orbicular muscle, the 

 sphincter vagina. The external organs of generation are the clitoris, the 

 labia internet, or nymphce; and, the labia externa or pudenda, formed of the 

 external integument, and lined internally by mucous membrane. Numerous 

 mucous follicles are scattered beneath the mucous membrane of the external 

 organs of generation; and two larger lobulated glands, the glands of Bar- 

 tholin, analogous to Cowper's glands in the male, are located at the sides 

 of the lower part of the vagina. The ducts of these glands are about 12 mm. 

 long and open immediately external to the hymen at the mid- point of the 

 lateral wall of the vaginal orifice. 



Ovulation and Menstruation. In the process of development in the 

 ovary, the individual vesicular ovarian follicle increases in size and gradually 

 approaches the surface of the ovary. When fully ripe or mature, it forms a 

 little projection on the exterior. Coincident with the increase in size, which 

 is caused by the augmentation of its liquid contents, the external envelop 

 of the distended vesicle becomes very thin and eventually bursts. The ovum 

 and fluid contents of the vesicle escape on the exterior of the ovary, whence 

 they pass into the uterine tube. 



In man and mammals ovulation apparently occurs only at certain periods. 

 These periods seem to precede or occur during the changes in the woman 

 that constitute the phenomenon of menstruation, or, in the lower mammals, 

 of heat. 



That ovulation and discharge occur periodically, and only during the 

 phenomenon of heat, in the lower mammalia, is made probable by the facts 

 that, in all instances in which ovarian vesicles have been found presenting 

 the appearance of recent rupture, the animals were at the time or had recently 



