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Show 1889.] THE BODY-CAVITY IN LIZARDS, ETC. 461 Figs. 8, 9, and 10 show this right-hand sac at the beginning of the 9th day, and we see (fig. 10,/. TV.) that the foramen of Winslow is still open. But on the 9th day this foramen becomes closed (that is, I could find no aperture in a complete series of sections of a chick of 9 days 1 hour incubation), and moreover that part of the recess which surrounds the gizzard, as opposed to the oesophagus, becomes obliterated1 (compare fig. 12, 2, with fig. 10, 2), This space (2), which can be followed through the sections of the 12th day (cf. figs. 14-17 and 26-28) and seen in those of the adult fowl (figs. 44-46), corresponds, as stated, to rather more than the "recessus superior sacci omenti" of Mammals, since its posterior part represents a portion of the omental sac. For this reason, and because there is a similar space on the left side (where there is no omental sac to have a recess), and because these spaces are in fact no mere diverticula of the omental sac, but have a distinct origin, I have spoken of them as the pulmohepatic recesses (cf. ante, p. 454). This name expresses their relation to the liver and respiratory organs, and to the pulmohepatic ligaments which form part of their outer wall. In the fowl the foramen of Winslow up to the 9th day, when it closes, has precisely the same relations as in Mammals, being bounded by the inferior vena cava antero-dorsally, and the duodeno-hepatic omentum, or ventral mesentery that bears the bile-ducts and portal vein, postero-ventrally. With regard to the corresponding recess on the left side (2' in the figures previously referred to), a reference to the figures shows that it is from the first in much freer communication with the rest of the peritoneal cavity than that on the right, and the alimentary canal, instead of (as in the case of the other recess) bending round to form, together with the median vertical membrane that supports it (m, figs. 9, 12, 14, 15), a posterior or omental wall, appears rather on the contrary to hinder the development of its outer wall by leaning over on the left side between the lung and liver. III. (d). On the Homology of the Avian and Mammalian Diaphragms. O n considering the relations of the recesses and ligaments (2, 2', a, a.) in the two above-named groups, we see that the whole of the Mammalian diaphragm lies laterally or centrifugally to the attachments (a, a) of the liver to the mediastinal tissues in front of it, while the avian diaphragm lies practically entirely within or centripetally to these attachments. So that the condition in birds is expressed by saying that the middle mediastinal tissue of the two sides, instead of coming to wrap round the pericardium, diverges posteriorly and ventrally to become attached to the lateral body-walls2. 1 Apparently by constriction off from the rest and the adhesion of its walls. 2 W e may, for illustration, compare the middle mediastinal tissue of birds in its relation to the pericardium to a coat which, instead of being buttoned across the chest (the pericardium), is extended like a wing on either side by laying hold of the front bottom corners. |