The Uterine Tubes
The uterine tube measures about 20 cm when extended but in nature follows a tortuous course that brings its beginning and end close together. The infundibulum is margined by ragged fimbriae that spread over the surface of the ovary, where some make permanent attachment (Fig.
22.11/2). A small opening in the depth of the infundibulum leads to the ampulla (Fig. 22.11/3), which is approximately 10 cm long and about 6 mm wide; its caliber at all stages of the cycle is greater than that of the isthmus, which is only half as wide. The isthmus (Fig. 22.11/4), also about 10 cm long, opens into the apex of the uterine horn through a small orifice on the summit of an eccentrically placed papilla. Strangely, this uterotubal junction is able in some way to distinguish between fertilized and infertile ova to allow entry to only fertilized eggs. The tubal mucosa is plicated, especially within the ampulla, where the elaborate major folds carry secondary and even tertiary ridges. The mesosalpinx, which supports the tube, branches from the lateral surface of the mesovarium and, with this, encloses a large but shallow ovarian bursa (Fig. 22.11/9 and see Fig. 5.60B/5).
FIG. 22.10 Sections of ovaries in various functional states. (A) Ovary with corpora lutea and small follicles. (B) Ovary with developing corpus luteum. (C) Ovary with fully developed corpus luteum. (D) Ovary with mature follicle. (E) Ovary with follicles of various sizes and a rather large corpus luteum. The corpus luteum of the mare does not protrude from the ovary as in other species. 1, Corpora lutea; 2, follicles; 3, blood vessels; 4, ovulation fossa.
FIG. 22.11 The right ovary, uterine tube, and uterine horn; lateral view. 1, Ovary; 2, infundibulum with fimbriae; 3, ampulla of uterine tube; 4, isthmus of uterine tube; 5, uterine horn; 6, mesovarium; 7, mesosalpinx; 8, mesometrium; 9, entrance to the ovarian bursa.