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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![the pharyngeal or branchial sac are in contact, they usually communicate by perforations between the bars of the sac, and the vessels in the bars may be looked upon as so many lines of perivisceral cavity included between the two else- where-adherent membranes. This, at least, would be the result of the views advocated by Carpenter, Huxley, and others, who consider that the atrium arises primarily in an inversion of the integument around the anal orifice, and that this inversion gradually insinuates itself among the internal organs, leaving only a very narrow external passage. Professor Allman, on the other hand, sees in an Ascidian the homologue of a retracted Hippocrepian Polyzoon, with the lophophore (always tilted in retraction) turned into the dorsal vertical vessel or sinus, and the tentacles forming the transverse bars of the branchial sac; the epistome being represented by the languettes. Mr. Hancock, who at first adopted Mr. Allman's ideas, has recently given a very careful analysis of the anatomy of the branchial chamber, upon which he founds conclusions tending to prove homology between the chamber, or, at least, parts of the chamber, and the gills of the Lamellibranchiata. He describes the true branchial organ as formed by two lateral plates or laminse transversely and longitudinally barred, separated dorsally from each other by two longi- tudinal folds of the lining membrane (atrial tunic), between which the endostyle is found at the bottom of a deep groove ; separated ventral]y from each other by another longitudinal fold, forming the -ventral lamina^^ along which food runs, collected into strings, to the mouth (oesophageal orifice). Above and below—at lines of anterior and posterior collars or cords —the laminse are firmly attached to the lining membrane, but elsewhere, excepting at the two vertical lines just mentioned, are free, being linked to the lining membrane by muscular suspenders.](https://iiif.wellcomecollection.org/image/b20410396_0096.jp2/full/800%2C/0/default.jpg)
