Mucous follicles are only found in the cervix, especially at its lower part: when by chance these become inflamed, the orifice closes, and the follicle becomes more or less distended by a collection of thin fluid. The mucous casts of these follicles have been known by the name of _ovula Nabothi_, having been mistaken by an old anatomist for Graafian vesicles, which had been detached from the ovary, and conveyed into the cavity of the uterus. The mucous membrane which lines the cervix uteri is corrugated into a number of rugæ, between which the mucous follicles are chiefly found. [Illustration: Uterus duplex.] Before quitting this subject, it will be necessary to point out the changes which the uterus presents at different periods of foetal life, and the great resemblance it has at these periods to the uterus, as it appears in the lower classes of the mammalia. We may, however, observe in the first place, that the uterus is not found to exist as a separate organ until we come to the class mammalia; and even in the lower genera of this class it bears a strong resemblance to the tubular character of the generative organs in the inferior classes of animal life. The nearest to the tubular uterus, and where the transition from the oviduct in birds, &c. to the uterus in mammalia is least distinctly marked, is in the _uterus duplex_. Although the uterus is double, there is but one vagina into which the two ora uteri open; its low grade of development is marked by the resemblance which each uterus bears to an intestinal tube: there are as yet no traces of a cervix, each os uteri merely forming a simple opening at the lower end of what is little more than a cylindrical canal. We do not find that thickening at the lower extremity of the uterus which distinguishes the cervix in the higher mammalia. This species of uterus is found among a large portion of the rodentia, and is also occasionally met with as an abnormal formation in the human subject. The next grade of uterine development appears under the form of the _uterus bicollis_. The double os uteri here ceases to exist, and the division begins a little higher up, so that the two cavities of the uterus communicate for a short space: the ova, however, do not reach the common cavity, but remain each in its separate cornu. In this form of uterus, the os uteri is not only single, but the lower portion is thickened, although it has not yet formed a distinct neck or cervix; it is met with among some of the rodentia, and also certain carnivora. [Illustration: Uterus bicollis.] [Illustration: Uterus bicorporeus.]