THE UTERUS 601 



The two horns are commonly unsymmetrical in length and diameter in mares which have borne 

 young. 



The body of the uterus (Corpus uteri) is situated partly in the abdominal, 

 partly in the pelvic, cavity. It is cylindrical, but considerably flattened dorso- 

 ventrally, so that in cross-section it is elliptical. Its average length is seven or 

 eight inches (ca. 18-20 cm.), and its diameter, when moderately distended, about 

 four inches (10 cm.). Its dorsal surface (Facies dorsahs) is related to the rectum 

 and other parts of the intestine. Its ventral surface (Facies ventralis) is in contact 

 with the bladder, and has inconstant relations with various parts of the intestine. 

 The term fvindus uteri is applied to the wide anterior part from which the cornua 

 diverge. 



The position of the body of the uterus is variable, especially in regard to its anterior part. 

 It is often pressed up against the rectum, and may be deflected to either side — most frequently 

 to the left — by the pelvic flexure of the great colon or coils of the small colon. 



The neck or cervix of the uterus (Cervix uteri) is the constricted posterior 

 part which joins the vagina. It is about two to three inches (5-7.5 cm.) in length, 

 and an inch and a half (3.5^ cm.) in diameter. Part of it (Portio vaginalis uteri) 

 projects into the cavity of the vagina; it is therefore not visible externally, but 

 may be felt through the vaginal wall. 



Attachments. — The body and horns are attached to the abdominal and pelvic 

 walls by two extensive peritoneal folds, the broad ligaments of the uterus (Liga- 

 menta lata uteri) . These extend on either side from the sublumbar region and the 

 lateral pelvic walls to the dorsal border of the cornua and the lateral margins of the 

 body of the uterus. They contain the vessels and nerves of the uterus and ovaries, 

 connective tissue, and a large amount of unstriped muscular fibers which are con- 

 tinuous with those of the uterus. The ureters are situated along their parietal 

 margins. The lateral layer of each gives off a fold, the round ligament of the uterus 

 (Ligamentum teres uteri), which blends with the parietal peritoneum over the 

 abdominal inguinal ring; its anterior extremity is situated above the extremity of 

 the cornu and forms a long round appendix. It contains muscular tissue, vessels, 

 and nerves, and is the homologue of the gubernaculum testis. The anterior part of 

 the neck is continuous with the vagina, and thus has a more fixed position than the 

 rest of the organ. 



The cavity of the uterus (Cavum uteri) is largely obliterated in the non- 

 pregnant state by the contraction of the wall and by folds of the mucous lining. 

 At the extremity of each cornu it communicates with the uterine tube by a minute 

 opening on a small papilla. The cavity of the neck is termed the cervical canal 

 (Canalis cervicis); it is closed ordinarily by mucous folds and a plug of mucus. 

 It opens into the vagina by the orificium externum uteri,i and into the body by the 

 orificium internum uteri. 



Structure. — The wall of the uterus consists of three coats. The serous coat 

 (Perimetrium) is, for the most part, closely adherent to the muscular coat. It is 

 continuous with the broad ligaments. The muscular coat consists essentially of 

 two layers, a thin external stratum of longitudinal fibers, and a thick internal layer 

 of circular fibers. Between these is a very vascular layer (Stratum vasculare) of 

 connective tissue with circular and oblique muscular fibers in it. The circular coat 

 is very thick in the neck, where it forms a sphincter half an inch or more (ca. 1.5 cm.) 

 in thickness. The mucous membrane rests directly on the muscular coat, and is 

 brownish-red in color, except in the neck, where it is pale. It is covered by a single 

 layer of high columnar cells, and contains numerous long, branched tubular uterine 

 glands (Glandulse uterinse) ; these are absent in the cervix. 



Vessels and Nerves. — The chief arteries are the uterine and the uterine 

 branch of the utero-ovarian, which have a flexuous course in the broad ligaments; 

 ^ This is frequently designated the os uteri. 



