File:Image from page 654 of "On the anatomy of vertebrates (electronic resource)" (1866) (14753299414).jpg

Identifier: b20416039_001 Title: On the anatomy of vertebrates [electronic resource] Year: 1866 (1860s) Authors: Owen, Richard, 1804-1892 Subjects: Anatomy, Comparative Vertebrates Fishes Reptiles Mammals Birds Publisher: London : Longmans, Green Contributing Library: Wellcome Library Digitizing Sponsor: Wellcome Library

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Text Appearing Before Image: der surface of the body. All the Plagiostomes have the external as well as the internaldivision of the vitellicle, fig. 425 ;the peduncle of the external oned, is longer, in some species con-siderably so, than in OsseousFishes, and it is beset with villiin Carcharias and ZygcBna.1The tegumentary covering of theouter yolk, ib. d!, is denser andmore opake in Plagiostomes:the inner yolk, ib. e, is co-vered only by the proper vitel-line tunic, which is thin andtransparent: it communicateswith the short tract of smallintestine which intervenes be-tween the pylorus and the val-vular straight gut, h : it receivesthe external yolk, df, as this isprogressively squeezed into the abdomen by the contractionand interstitial absorption of its tunics, c: and, as no part of thefoetal abdominal appendage is cast off, nor the chord divided, thereis no cicatrix—no umbilicus. The arterial vessels of the yolk arederived, not from the mesenteric vein as in Osseous Fishes, but 1 cxxui. tf. iii.VOL. I. R R

Text Appearing After Image: Embryo Cartilaginous fish, Scyllium. 610 ANATOMY OF VERTEBRATES. 426 from ramifications of a branch of the mesenteric artery, and theblood is returned to the mesenteric vein. Hunters preparationsof the embryo Carcharias (No. 1061), ScyIlium (No. 3250),Spinax (No. 3255), and Alopias (No. 3261) l, demonstrate anotherfoetal peculiarity which later researches 2 have shown to be pro-bably common to all Plagiostomes, viz. the external fringe offilaments developed from the branchial surfaces, b: a tuft extendsout of each aperture, and even from the spiracula, a, in the generawith those accessory openings. Each filament contains a single ca-pillary loop : 3 they disappear early, being removed by absorption.The last remnants may be seen in the preparation of the foetal Saw-fish (Pristis, No. 3263),4 which is eight inches in length, includingthe saw, and has the duct of the external vitellicle attached. Inthe oviparous Sharks, the branchial filamentsreact on the streams of water admitted into t

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