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Show 464 MR. G. W. BUTLER ON THE SUBDIVISION OF [Nov. 19, side there is still a communication (*) between the hepatic and post-hepatic parts of the abdominal cavity; and comparing this with figs. 15 & 17, which represent sections respectively dorsal and ventral to the section in fig. 16, it will be seen that the more dorsal part of the post-hepatic septum is composed of the oblique abdominal septum (y), while the more ventral part consists of the lateral " omental" extension (/3). On the left side the ventral and dorsal components of the post-hepatic septum never meet, and there is always in the fowl a free communication between the " pulmohepatic recess " of this side and the general intestinal cavity. In the duck this is reduced to the condition of a small aperture (cf. supra, p. 454). With regard to the origin of this post-hepatic septum, it would seem that the ventral portion (/3) is, so to speak, started by the vitelline veins which cause considerable inward projections of the lateral body-walls in which they run. With the closing-in of the body-wall in the region of the umbilicus, the vessel of the left side which alone continues as the allantoic vein (or in the adult as an anterior abdominal vein carrying blood from the fat-laden omentum) comes to assume a more central course, but the ventro-lateral attachment of the membrane which supported these vessels persists. The dorsal component (y) of the post-hepatic septum, on the other hand, is due to the extension laterally and posteriorly, by the growth of the abdominal air-sacs, of the ridge that forms a backward continuation of the pulmonary tissue of either side. And it is thus that I believe that in those Sauropsida which have no similar arrangement of air-sacs the post-hepatic septum, which may be present (Crocodiles and Teiidae), is the homologue of the ventral component of this septum in the bird-the dorsal part being merely represented by the membranous fold, which in many Lizards extends for a considerable distance behind the lungs. IV. ON THE BODY-CAVITY OF THE LACERTILIA AND OF THE TEIIDAE IN PARTICULAR. (a) The Lacertilia generally. Turning now to the Lacertilia and recurring to the question of the ventral attachment of the lungs. The left lung seems to have, as a rule, its ventral border but slightly if at all attached, but there is sometimes a short ligament connecting this with the liver or tissue in front of that organ. The right lung, on the other hand, seems as a rule (cf. p. 465, fig. A ) to have its whole ventral border attached to the dorsal wall of the right liver-lobe, or-seeing that dorsally it is attached to the middle line by another ligament-it may sometimes be rather described as set on the outer side of a membrane passing between the right liver-lobe and the dorsal part of the median mesentery. The spaces thus enclosed between the lung and its ligaments on the outside, and the oesophagus and its ligaments in the middle line, are homologous with the pulmohepatic recesses of birds above described |
