The early development of the pericardium, diaphragm, and great veins / by C.B. Lockwood.

  • Lockwood, Charles Barrett, 1856-1914.
Date:
1888
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Licence: Public Domain Mark

Credit: The early development of the pericardium, diaphragm, and great veins / by C.B. Lockwood. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    they protrude into the recessus abdomiiialis, so that it has also been called by His the recessus pulmonalis.* * * § Further, it can easily be perceived that the iter venosum corresponds to the passage which in many Vertebrates, especially the Skate and Dog- fish, unites the pericardium with the rest of the body cavity, and whose origin, Balfour says, has not been satisfactorily worked out.t It may be inferred from the foregoing that the iter venosum is bounded ventralwards by the vitelline vein, dorsal- wards by the body wall, externally by the mesocardium laterale, and internally by the splanchnopleure, where that membrane is closing in behind the venous end of the heart to form the fore-gut and mesocardium posterius (figs. 16b and 20c, It. F.). Behind the heart and vitelline veins the splanchnopleure has not as yet infolded to form the alimentary canal, but runs outwards on either side to unite with the somato- pleure (figs. 17b and 18b, Spl.). Longitudinal sections near the axis of the embryo and internal to the iter show the heart in its relation to the pharynx (figs. 13a and 14a), and their appearances have been rendered familiar by Kolliker,| Uskow, and others. Taken alone, they suggest that the heart lies in a separate and distinct chamber of its own ; but such an idea is shown to be erroneous, both by earlier embryos and by the other sections through the iter. The appearance seems due to the fact that in the cardiac region the halves of the coelom have already coalesced, whilst behind they are still apart; so that, in consequence, the splanchnopleure which spreads outwards from one to the other envelops the venous end of the heart (fig. 14a), and thus seems to form a closed chamber for it. Soon after the heart has become an unpaired organ the ventral wall of the cardiac chamber alters so much that the share the splanchnopleure has in its formation is less obvious. It seems reasonable to infer that, inasmuch as its ventral boundary wall is covered with hypoblast, therefore it is of splanchnic origin, and this is borne out by the younger embryos (figs. 1 to 3, Hy.). In longitudinal sections, as Van Beneden and Julin also show, the hypoblast extends forwards over the ventral wall of the cardiac coelom to form, with the epiblast, the pro-amnion (fig. 5, P. am.). Authorities are agreed that the mesocardium laterale plays an important part in the development of the pericardium, but some of its features, I think, require further elucidation. Its formation seems to be exceedingly constant in the vertebrate series, and it is recognised to be a junction of splanchnopleure to somatopleure, which serves for the transmission of the somatic venous system into the splanchnic. The former would, in the earlier stages of development, comprise the umbilical veins, the cardinal veins, and the Cuvierian ducts; the latter the vitelline veins and heart. The cj[uestion arises whether, as Kolliker§ and Balfour || seem to think, the * ‘ Anatomie Menschliclier Embrjonen,’ pt. 3, p. 146. t ‘ Comp. Embryo].’ vol. 2, p. 628. t Log. cit., pp. 407 et. seq. § Log. cit., p. 295. II Log. cit., vol. 2, p. 627.