File:Quain's elements of anatomy (1882) (14577266319).jpg

Identifier: quainselementsofquai02 (find matches)
Title: Quain's elements of anatomy
Year: 1882 (1880s)
Authors: Quain, Jones, 1796-1865 Thomson, Allen, 1809-1884 Sharpey-Schäfer, E. A. (Edward Albert), Sir, 1850-1935, ed Thane, George Dancer, 1850-1930
Subjects: Human anatomy Anatomy
Publisher: New York : William Wood and co.
Contributing Library: Francis A. Countway Library of Medicine
Digitizing Sponsor: Open Knowledge Commons and Harvard Medical School

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ts ofa set of segmental tubes developed in connection Avith this duct, pos-sessing the same glandular and glomerular structure as the mesonephros,and occupying a situation which is on the dorsal aspect of the Wolffianduct and near its hinder part. The characteristic feature in the develop-ment of the urino-genital system m the amniota is according to Balfourthe formation of a metanephros or permanent kidney, and the completeor partial disappearance of the other two parts of the segmental organs—viz., the pronephros and mesonephros. The Miillerian and Wolffian ducts stand in a different relation to theproductive organ in the two sexes. In the female the Miillerian ductbecomes developed into the whole length of the genital passages, and theWolffian duct almost entirely disappears. In the male, on the otherhand, the Wolffian duct becomes converted into the excretory duct (vasdeferens) of the testicle ; while the Miillerian duct undergoes atrophy andhas no permanent existence. Fig. 801.
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Fig. 801.—Diagram of the arrangement of the ureno-genital organs in an ADULT female ELASMOBRANCH (from Balfour). m.d., Müllerian duct; w.d., Wolffian duct; s.t, segmental tubes; five of them are represented with openings into the body cavity, and five posteriorly correspond to themetanephros ; ov, the ovary ; d, ureter.

In connection with the conducting passages of both sexes there are found in later life vestiges of those of the embryonic structures which are not employed in the production of the permanent generative organs, and these vestiges are of considerable interest in their bearing upon the history of the changes by which the permanent organs are formed. Genital Ridge and Germ-Epithelium.—In all the Vertebrates the productive gland of the generative system, ovary or testicle, takes its morigin from formative blastema situated on the mesial side of each Wolffian body or mesonephros at an early period of embryonic life, and there is in the commencement a close connection between the origin of the first elements of the sexual products, ova or spermatic cells, and a portion of the epithelium which lines the body cavity in that region. Here an elevation of the blastema and thickened epithelium marks the presence of the genital ridge, and the name of germ-epithelium.

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