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 cesophagus) 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 trans- 
versa”’” and ‘ Massa longitudinalis” *, 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 out- 
ward 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 (pulrmohepatic 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. 208, 
when describing a comparatively late stage) so far the rabbit and 
1 “Nicht so bei Huhn. Hier hingt die Massa longitudinalis mit der trans- 
versa nicht im medianen Bezirke, sondern nur rechts und links zusammen mit 
je einem Schenkel...... Sie gleicht also einer medianen Leiste, welche 
caudalwarts sich in 2 schenkel spaltet; diese fassen einen Kopfwiirts vorgescho- 
benen zipfel der Peritoneal héhle zwischen sich. In diesem zipfel liegt die 
dorsal flache 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 Dorsaltfiiche 
der beiden seitlichen Schenkel der Letzteren befestigt sind, so ergibt sich das 
es nicht leicht ist in den eben erwahnten Bildungen das Mittelstiick des 
dorsalen diaphragmas des Kaninchens wieder zu finden...... 
“Der ganze unterschied zwischen der Entwickelung des Huhns und des 
Kaninchens kann demgemiiss fiir diese Periode so formulirt werden: Beim 
Kaninehen legt sich das mittelstiick des dorsalen Diaphragmas lings den 
Dorsalflache der Leber, beim Huhn lings der Ventralfliche der Lungen an,” 
2 Defined Z. c. p. 171. 
* Defined Z. ¢. p. 172. 
