The main channels by which the blood is returned to the heart. The right hepatocardiac vein is shown particularly well. The coelomic surface over it is modified in a manner that increases the permeability between the coelom and this channel as it empties into the sinus venosus. This greater permeability is most marked at this stage and disappears later. Based on Born reconstructions of No. 836, made by Osborne O. Heard under the supervision of H.M. Evans.

[The above text and accompanying figure are taken from O'Rhailly, R., and Müller, F.. Developmental Stages in Human Embryos, Carnegie Institution of Washington, Publication 637, 1987.]

[adapted from figure 13-3]