. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. UTERUS-(DEVELOPMENT). 653 upon the arrival of the ovum within the ute- rine cavity are, in the human subject, as yet unknown. Direct observation of the earliest stages are still wanting, and, unfortunately, the difference between these first steps in the mammalia (except Quadrumana) and man is so considerable, that only a limited aid can be derived from comparative observation. The ovum, when first found in the human uterus, is lodged in a small closed cavity, forming a continuous structure with the decidua which lines t
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. UTERUS-(DEVELOPMENT). 653 upon the arrival of the ovum within the ute- rine cavity are, in the human subject, as yet unknown. Direct observation of the earliest stages are still wanting, and, unfortunately, the difference between these first steps in the mammalia (except Quadrumana) and man is so considerable, that only a limited aid can be derived from comparative observation. The ovum, when first found in the human uterus, is lodged in a small closed cavity, forming a continuous structure with the decidua which lines the rest of the uterine walls. In this little chamber, which may be formed at any part, but is most frequently seen near one or other of the tubal orifices, the little spherical ovum lies loose and unattached. In various examples which have been preserved and figured by different authors of the decidua at tfais stage, the size of this chamber varies from that of a pea to a hazel nur, and this size it acquires in the second week. The walls of the cavity containing the ovum, and those forming the lining membrane of the uterus, are nearly alike in appearance and texture. They both consist of decidua, the former constituting the decidiirt reflexa, the latter the decidua vera of Dr. W. Hunter. For greater distinctness, those names are sometimes exchanged for decidua e/iorii or ovu/i, and decidua uteri. The latter, accord- ing to a suggestion of Dr. M. Baillie, is also occasionally termed parietal decidua. At this time all the uterine tissues have begun to expand and grow, and the uterine cavity, the walls of which were previously nearly in contact, to enlarge after the manner which in pathology constitutes eccentric hy- pertrophy. But, according to the foregoing description, this cavity now no longer forms one, but two compartments, the one partly inclosed within the other. Of these two chambers, the newly formed and smaller one contains and supports the ovum, and subsequently the f
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