Notes on comparative anatomy : a syllabus of a course of lectures delivered at St. Thomas's Hospital / by William Miller Ord.
- William Miller Ord
- Date:
- 1871
Licence: Public Domain Mark
Credit: Notes on comparative anatomy : a syllabus of a course of lectures delivered at St. Thomas's Hospital / by William Miller Ord. Source: Wellcome Collection.
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![Internally, each somite ty[ucally contains a marked segment of alimentary canal, a pair of nervous ganglia, a definite division of circulatory system, a proper set of muscles, and distinct reproductive organs. Anterior somites ; cirrhi developed, and acquire title of tentacula; setae and acicula dwarfed or lost. First few somites more or less fused to form a head; the mouth placed on the inferior aspect of 2nd, 3rd, or 4th. Posteriorly similar but less pronounced changes. Anus opens usually on inferior surface of last somite but one. Muscular system.—Muscles connected with external skele- ton and oars, numerous, and regularly arranged. Alimentary Canal.—Usually runs through the body in one straight line without flexure or convolutions. Usually exhibits a dilatation corresponding to each somite, and linked to its walls by delicate mesenteries. These segmental dilatations often also send off branch- ing diverticula. (Aphrodite.) At commencement of alimentary canal often a pro- boscis, formed by a very muscular evertible pharynx; supporting hooks or teeth ; teeth (sometimes called jaws are placed on each side of the mouth, and work in horizontal plane. Salivary glands C?) of Nereis. Hepatic function (]) of csecal diverticula. Blood, and perivisceral cavity.—Fluid, filled with small oat-shaped corpuscles; surface ciliated: no heart; distribu- tion of fluid by cilia and by movements of body; all the tissues bathed in this fluid. Pseudo-hsemal system.—A system of closed contractile vessels, usually much convoluted and exhibiting many dilata- tions—so-called hearts—which have, however, no extra thickness of wall. They contain a non-corpusculated, trans- parent fluid, variously coloured, and propelled by peristalsis](https://iiif.wellcomecollection.org/image/b20410396_0036.jp2/full/800%2C/0/default.jpg)
