THE REPRODUCTIVE SYSTEM. 639 



the uterus, of fibrous tissue and unstriped muscular fibres, chiefly circu- 

 lar in arrangement. 



c. The Uterus. The Uterus (u, c, Fig. 424) is somewhat pyriform, 

 and in the unimpregnated state is about three inches in length, two in 

 breadth at its upper part or fundus, but at its lower pointed part or 

 neck, only about half an inch. The part between the fundus and neck 

 is termed the body of the uterus: it is about an inch in thickness. 



Structure. The uterus is constructed of three principal layers, or 

 coats serous, fibrous andt muscular, and mucous. (1.) The serous coat, 

 which has the same general structure as the peritoneum, covers the 

 organ before and behind, but is absent from the front surface of the 

 neck. (2.) The middle coat is composed of unstriped muscle, arranged 

 in the human uterus in three layers from without inwards, longitu- 

 dinal, circular, oblique and circular. They become enormously devel- 

 oped during pregnancy. The arteries and veins are found in large 

 numbers in the outer part of this coat, so as to form almost a special 

 vascular covering. (3.) The mucous membrane of the uterus is lined 

 by columnar ciliated epithelium, which extends also into the interior of 

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



In the neck of the uterus (cervix) the mucous membrane is arranged 

 in permanent longitudinal folds, palmaa plicatae, and between these folds 

 open the ducts of the tubular glands. In the fundus the proper tissue 

 is a spongy tissue of interlacing fibrous bundles, forming a system of 

 lymph channels. Here the lining is a single layer of flattened cells. 

 The tubular glands are usually simple and unbranched, and seldom wavy 

 or convoluted. 



The cavity of the uterus corresponds in form to that of the organ 

 itself: it is very small in the unimpregnated state; the sides of its mu- 

 cous surface being almost in contact. Into its upper part, at each side, 

 opens the canal of the corresponding Fallopian tube: below, it commu- 

 nicates with the vagina by a fissure like opening in its neck, the os uteri, 

 the margins of which are distinguished into two lips, an anterior and 

 posterior. In the mucous membrane of the cervix are found several 

 mucous follicles, termed ovulaor glandulae Nabothi: they probably form 

 the jelly-like substance by which the os uteri is usually found closed. 



The vagina is a membranous canal, five or six inches long, extend- 

 ing obliquely downwards and forwards from the neck of the uterus, 

 which it embraces, to the external organs 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. This exists also in the mucosa. The lower extremity of 



