Archive image from page 94 of The cyclopædia of anatomy and. The cyclopædia of anatomy and physiology cyclopdiaofana05todd Year: 1859 OVUM. [81] Ovum of Mammalia and of the Human Species. — There is a remarkable uniformity in the size, structure, and relations of the ovarian ovum in the whole class of Mammalia, with the exception of the families of Marsu- piata and Monotremata ; in the last of which especially there is an approach to the oviparous type. We shall first consider the more com- mon form of the mammiferous ovum. Of this the most marked characteristics are, as has already been stat
Archive image from page 94 of The cyclopædia of anatomy and. The cyclopædia of anatomy and physiology cyclopdiaofana05todd Year: 1859 OVUM. [81] Ovum of Mammalia and of the Human Species. — There is a remarkable uniformity in the size, structure, and relations of the ovarian ovum in the whole class of Mammalia, with the exception of the families of Marsu- piata and Monotremata ; in the last of which especially there is an approach to the oviparous type. We shall first consider the more com- mon form of the mammiferous ovum. Of this the most marked characteristics are, as has already been stated, the very small size in proportion to the ovarian follicle, the finely granular yolk-substance, and the dense, clear, and firm external covering or zona pellucida. The Graafian follicles, or ovarian vesicles, in which the ova are situated, attain, when mature, a size of from to or even 1 an inch, varying in size in some measure with, but not in exact proportion to, the stature of the animals. In the human ovary these fol- licles are firm spheroidal sacs, which attain when mature an average size of about of an inch. In the ovaries of women, during the child-bearing period, a number of smaller folli- cles lie throughout the greater part of the substance of the ovary ; the more developed follicles being usually placed towards the free surface, but at some little distance from it. As they enlarge and approach maturity, the ova- rian substance appears to give way to them, or to become gradually thinner between the follicles and the outer surface of the ovary, so as at last to leave almost nothing but the covering membranes of the ovary at the most projecting part. Even when of their full size, however, the Graafian follicles of the human subject and of most animals do not project much beyond the general surface of the ovary; Fig. 54. A Ufammiferous Ovum. A. (From Costs.) Human ovary enlarged four diameters, partially dissected at ooo, to show the Graafian follicles in t
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