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 connexiou with the latter takes, if any, but a 

 comparatively insignificant part in the closing-oflf 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 (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. 20.5, 

 when describing a comparatively late stage) so far the rabbit and 



^ "Kiclit so bei Hiihu. Hier hiingt die Massa longitudinalis mit der trans- 

 versa niclit iui ruedianen Bezirke, soudern nur rechts und links zusammen niit 



je einem Schenkel Sie gleicht also einer medianen Leiste, welcbe 



caudalwiirts sicb in 2 scbenkel spaltet; diese fassen einen KoptVarts vorgescbo- 

 beneu zipfel der Peritoneal bohle zwischen sicb. In diesem zipf'el liegt die 



dorsal fliicbe der Leber frei Nimiut man nocli liinzu, das die Lungen 



in der so bescbrankten paarigeu Huble der Pleura nicbt uiir an den Sagittal 

 rand der massa longitudinalis, sondern Tornebmlicla aucb an die Dorsalliiicbe 

 der beide.n seitlicbeu Scbenkel der Letzteren befestigt siud, so ergibt sicli das 

 es niclit leicbt ist in den eben erwabiiten Bilduiigen das Mittelstiick des 

 dorsalen diaphragmas des Kanincbens wieder zu linden 



" Der gauze unterscliied zwiscben der Entwickehmg des Hulms und des 

 Kanincbens kann demgemiiss fiir diese Periode so formulirt werden : Beim 

 Kanincben legt sich das mittelstiick des dorsalen Diapbragmas liings den 

 Dorsaliliicbe der Leber, beim Hubn liings der Ventralfliicbe der Lungen an." 



2 Defined I. c. p. 171. 



■* Defined I. c. p. 172. 



