The two uterine horns in the adult are joined caudally to form an externally undivided segment consisting of a cranial and a caudal part. The cranial part becomes wide and swollen at its junction with the horns. It contains two lumina separated by a midline septum and is designated as the uterine body or corpus. The narrow and slightly tapered caudal part projects into the cranial portion of the vagina. It contains a single lumen or canal and is designated as the uterine neck or cervix. The wall of the cranial two-thirds of the adult cervix contains a relatively large amount of circularly arranged smooth muscle fibers. In contrast, its caudal one-third consists chiefly of a network of collagen fibers. During cervical development argyrophilic fibers h s t appear in sections of cervical wall from mice sacrificed at birth. Collagen and smooth muscle fibers are first stainable with the Mallory method in cervical wall sections from mice one week old. During pregnancy and after combined treatment with estradiol, progesterone and relaxin the collagenous fiber bundles of the cervix become looser and more widely separated. This is associated with an increased dilatability of the cervical canal and increased stainability of the ground substance. The muccopolysaccharide( s) demonstrable histochemically in the cervix of the mouse was digestible with testicular hyaluronidase.Despite the numerous studies on the genital tract of the female mouse, decriptions of the normal gross and microscopic anatomy of the uterine cervix are inadequate. Eckstein and Zuckerman ('56) reviewed the anatomy of the reproductive tracts from several orders of mammals. Their description of the uterus of the mouse was very brief and lacked illustrations. In addition, the gross anatomical descriptions of the uterus of the mouse were related to the named parts of the human uterus. Because the simplex or human type of uterus represents the most extensive amount of fusion of the paramesonephric ducts during development, it is misleading to use similar terminology in naming the different regions of the bicornuate uterus of the mouse.In the experimental work on the cervices of other animals, DeVaal (' 46) and Uyldert and DeVaal ('47) first reported that the cervices of rats became progressively softer and more easily dilatable during pregnancy. These changes were not observed in the cervices of nonpregnant or estrogentreated rats. Softening and increased dilatability of the cervix during pregnancy and hormonal treatment occur in the cow (Graham and Dracy, '52, '53); sow (Zarrow et al., '54); monkey (Hisaw, '59) and the ANAT. REC., 150: 51-66.mouse (Steinetz et al., '56, '59; Crelin, '58; Kroc et al., '59). The cervices were not studied microscopically.
MATERIALS AND METHODSOne hundred and sixty-one Brown-belt stock mice were used. A study was made of the normal structure and development of the uterine cervices from 35 intact mice ranging in the age from 16 days prenatally to ten weeks post partum. Five mice were sacrificed on day 16 and 18 prenatall...
