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Show 462 MR. G. W. BUTLER ON THE SUBDIVISION OF [Nov. 19, According to this view, the " avian diaphragm " corresponds, as Huxley says of the oblique septum, to the middle mediastinum of Mammals. The pulmohepatic recesses form a pair of spacious sacs (instead of a single minute one), and the liver is attached to the mediastinal tissue by the pulmohepatic ligaments quite laterally (instead of merely round the oesophagus) along a line on either side very close to that of the attachment of the avian diaphragm itself to the body-wall. When following the completion of the partition between the pleural and peritoneal cavities of the bird, one observes a ridge which is connected with the Miillerian duct extending inwards from the body-wall to meet the outwardly extending mediastinal tissue. This is at once suggestive of the membrane bearing the Miillerian duct, or its continuation, which in the Amphibia and Lacertilia extends obliquely forwards along the lateral body-wall and ends near the ventral line of division between the lungs and liver. But although the avian diaphragm does become attached to the body-wall along the line of attachment of the embryonic Miillerian duct, the fold in connexion with the latter takes, if any, but a comparatively insignificant part in the closing-off of the pleural from the peritoneal cavity. Uskow (5, p. 204') expressing himself in terms of " Massa transversa" 2 and "Massa longitudinalis" 3, calls attention to just the points of contrast between Birds and Mammals that have been referred to above, viz. the lateral attachment of the liver, the outward diverging postero-ventrally of the mediastinal tissue, with the consequent dorsal as well as lateral projection of the lungs. He notes that the liver projects freely into forwardly extending portions of the peritoneal cavity (pulmohepatic recesses); and he finally states the fundamental difference between the central portion of the diaphragm of the chick of 7 days and the rabbit of 14 days to lie in the fact that in the former it goes with the lungs and in the latter with the liver. But, as remarked above, he goes on rather to compare than contrast the two types of diaphragm, saying (p. 205, when describing a comparatively late stage) so far the rabbit and 1 " Nicht so bei Huhn. Hier hangt die Massa longitudinalis mit der transversa nicht im medianen Bezirke, soudern nur rechts und links zusammen mit je einern Schenkel Sie gleicht also einer medianen Leiste, welche caudalwiirts sich in 2 schenkel spaltet; diese fassen einen Kopfwarts vorgescho-benen zipfel der Peritoneal hiihle zwischen sich. In diesem zipfel liegt die dorsal llache der Leber frei Nimmt man noch hinzu, das die Lungen in der so beschrankten paarigen Hohle der Pleura nicht nur an den Sagittal rand der massa longitudinalis, sondern vornehmlich auch an die Dorsalfiache der beiden seitlichen Schenkel der Letzteren befestigt sind, so ergibt sich das es nicht leicht ist in den eben erwiihnten Bildungen das Mittelstiick des dorsalen diaphragmas des Kaninchens wieder zu finden ^" Der gauze unterschied zwischen der Entwickelung des Huhns und des Kaninchens kann demgemass fiir diese Periode so formulirt werden: Beint Kaniucben legt sich das mittelstiick des dorsalen Diaphragmas langs den Dorsalfiache der Leber, beim H u h n langs der Ventralflache der Lmicen an." 2 Defined I. c. p. 171. 3 Defined I. c. p. 172. |
