OCR Text |
Show 454 MR. G. W. BUTLER ON THE SUBDIVISION OF [Nov. 1 9, of this latter septum enters into the dorsal wall of the sacs in question, for the anterior portion of this wall is formed by the liver-lobes (h, h') themselves, and by the ligaments (a, a) which pass from the liver to the more vertical portions of the " oblique septum." The lines of attachment of these ligaments to the oblique septum follow approximately the ventro-external margins of the lungs, where this latter membrane is apposed to them. The ligaments referred to may be called the pulmohepatic ligaments (a, a). I now call special attention to them because in the sequel I use them as a landmark in comparing the different types. On cutting through the pulmohepatic ligament there is exposed, on the right side, another entirely closed sac (Plate XLIX. figs. 44, 45, 46, 2), bounded externally by the more vertical portion of the " oblique septum," dorsally by the septum (y) above referred to, and in part by the more horizontal portion of tbe "oblique septum." The right liver-lobe (h, figs. 44 & 46) is attached to the dorsal wall of this sac from the point where the vena cava inferior enters it, backwards, and the sac is thus partially subdivided into two. In the Duck, the corresponding sac of the left side appears to be quite closed; but it really communicates with the post-hepatic or intestinal portion of the body-cavity by a small aperture, which is merely closed by the left "abdominal" air-sac flapping against it. In the Fowl, however, the continuity of this sac with the intestinal cavity is plain, its hinder end being freely open. These two sacs in the Bird, which are partly bounded by the pulmohepatic ligaments ventro-laterally, I will call the pulmohepatic recesses, and their homologies will be referred to later (p. 460, § III. c). For a capital description of the avian diaphragm reference may be made to Sappey (1, pp. 21-26), also to the ' Comparative Physiology ' of Milne-Edwards (vol. ii. p. 401) and to Huxley (4). All three accounts accord perfectly. Milne-Edwards's, in fact, differs little from Sappey's, even in nomenclature. Huxley introduces a few new terms, such as pulmonary aponeurosis (for the plan transversal or diaphragme pulmonaire of Sappey, the diaphragmite anterieure of Milne-Edwards), and oblique septum (for the plan oblique or diaphragme thoraco-abdominal of Sappey, diaphragmite posterieure of Milne-Edwards). I here use Huxley's terms for these two parts of the diaphragm. I assume that the general relations of these two membranes and their air-sacs, which he and Sappey have so clearly described, require no explanation on my part. Sappey makes it very clear that he regards the two membranes the abdominal air-sacs, " E n bas et en avant ils s'appuient sur une cloison fibreuse qui divise chez tous les oiseaux la cavite abdominale en deux cavites plus petites, l'une anterieure, qui represente l'abdomen et qui loge le foie, l'autre posterieure' qui represente le bassin et qui loge l'estomac et les intestines ; cette cloison fibreuse extremement remarquable dans l'autriche oil elle a ete decrite par Perrault sous le n o m de diaphragme transversal, s'insere a toute la circonference des os du bassin, et soutient l'estomac ainsi que le tube intestinal." It will be noted that the two sacs I a m describing form only the ventral portion of the anterior cavity of which Sappey here speaks. |