THE UTERUS. 1031 



that portion of the cavity which corresponds to the body is triangular, flattened 

 from before backward, so that its walls are closely approximated, and having its 

 base directed upward toward the fundus. At each superior angle is a funnel- 

 shaped cavity, which constitutes the remains of the division of the body of the 

 uterus into two cornua, and at the bottom of each cavity is the minute orifice of 

 the Fallopian tube. At the inferior angle of the uterine cavity is a small con- 

 stricted opening, the internal orifice (ostium internuni), which leads into the cavity 

 of the cervix. 



The cavity of the cervix is somewhat fusiform, flattened from before backward, 

 broader at the middle than at either extremity, and communicates below with the 

 vagina. The wall of the canal presents, anteriorly and posteriorly, a longitudinal 

 column, from which proceed a number of small oblique columns, giving the appear- 

 ance of branches from the stem of a tree ; and hence the name arbor vitce uterina 

 applied to it. These folds usually become very indistinct after the first labor. 



Structure. The uterus is composed of three coats : an external serous coat, a 

 mid.lle or muscular, and an internal mucous coat. 



The serous coat is derived from the peritoneum ; it invests the fundus and the 

 whole of the posterior surface of the uterus ; but covers the anterior surface only 

 as far as the junction of the body and cervix. In the lower fourth of the posterior 

 surface the peritoneum, though covering the uterus, is not closely connected with 

 it, being separated from it by a layer of loose cellular tissue and some large 

 veins. 



The muscular coat forms the chief bulk of the substance of the uterus. In 

 the unimpregnated state it is dense, firm, of a grayish color, and cuts almost like 

 cartilage. It is thick opposite the middle of the body and fundus, and thin at 

 the orifices of the Fallopian tubes. It consists of bundles of unstriped muscular 

 fibres, disposed in layers, intermixed with areolar tissue, blood-vessels, lymphatic 

 vessels, and nerves. In the impregnated state the muscular tissue becomes more 

 prominently developed, and is disposed in three layers external, middle, and 

 internal. 



The external layer is placed beneath the peritoneum, disposed as a thin plane 

 on the anterior and posterior surfaces. It consists of fibres which pass trans- 

 versely across the fundus, and, converging at each superior angle of the uterus, 

 are continued on the Fallopian tube, the round ligament, the ligament of the 

 ovary : some passing at each side into the broad ligament, and others running 

 backward from the cervix into the sacro-uterine ligaments. 



The middle layer of fibres, which is thickest, presents no regularity in its 

 arrangement, being disposed longitudinally, obliquely, and transversely. It con- 

 tains most blood-vessels. 



The internal or deep layer consists of circular fibres arranged in the form of 

 two hollow cones, the apices of which surround the orifices of the Fallopian tubes, 

 their bases intermingling with one another on the middle of the body of the uterus. 

 At the internal os these circular fibres form a distinct sphincter. 



The mucous membrane is thin, smooth, and closely adherent to the subjacent 

 tissue. It is continuous, through the fimbriated extremity of the Fallopian tubes, 

 with the peritoneum, and through the os uteri with the lining of the vagina. 



In the body of the uterus it is smooth, soft, of a pale red color lined by colum- 

 nar ciliated epithelium, and presents, when viewed with a lens, the orifices of 

 numerous tubular follicles arranged perpendicularly to the surface. It is unpro- 

 vided with any submucosa, but is intimately connected with the innermost layer 

 of the muscular coat, which is regarded as the muscularis mucosae. In structure 

 its corium differs from ordinary mucous membrane, consisting of an embryonic 

 nucleated and highly cellular form of connective tissue in which run numerous 

 large lymphatics. In it are the tube-like uterine glands, which are of small size 

 in the unimpregnated uterus, but shortly after impregnation become enlarged, 

 elongated, presenting a contorted or waved appearance toward their closed extrem- 



