224 MISS M. POOLE ON THE DEVELOPMENT OF THE _ [ Mar. 2, 
IJ. Aputr Anatomy. 
The Post-pulmonary Septum. 
Bertelli [8] gives an extremely clear description, accompanied 
by an excellent drawing, of his “diaframma ornitico” in the 
Fowl, with the attachments of all the costo-pulmonary muscles. 
Since, however, Sappey [16] has given such an elaborate account 
of the whole post-pulmonary septum in the Duck, and Huxley [12] 
has done the same in Apteryx, I do not propose to go over the 
same ground again here. But as—in spite of the recent embryo- 
logical work on the subject—there appears to be still some 
uncertainty as to the nature of the cavity within the post- 
pulmonary septum (that is to say between the pulmonary apo- 
neurosis and oblique septum of Huxley), it may be as well to 
point out those parts of the descriptions given by Huxley and 
others which embryology has shown to be incorrect. 
Huxley [12] in describing very clearly the partition which 
shuts off from the general visceral cavity a space enclosing the 
lungs and either most or all of the air-sacs on each side, appar- 
ently assumes, like Sappey, that this partition consists of two 
distinct septa, between which lies a cavity which is a division of 
the celom. For between the pulmonary aponeurosis dorsally 
and laterally, and the oblique septum ventrally and posteriorly, 
the lateral body-wall and the median dorsal septum, Huxley 
describes a space which he calls the subpulmonary chamber. 
This, he says, “is divided into four loculi by three dissepiments, 
which pass transversely from the lateral face of the oblique 
septum to the mesial face of the pulmonary aponeurosis. Each 
loculus lodges one of the four postbronchial saccular diverticula 
of the wall of the lung, constituting the proper air-sacs, which 
thus fill up the subpulmonary chamber, between the insertion of 
the bronchus and its posterior extremity. .... Thus, that part of 
the thoraco-abdominal cavity which lies dorsad and anterior to 
the oblique septum lodges no other viscera than the lungs and the 
air-sacs, and may be distinguished as the respiratory cavity, from 
the cardio-abdominal cavity which contains the heart and the rest 
of the viscera, and lies below and behind the oblique septum. 
The respiratory cavity is further divided into two lateral chambers 
by the median dorsal septum; and each of these chambers is 
subdivided by the pulmonary aponeurosis into two stories, of 
which the upper is occupied by the lung, and the lower by the 
loculi with their contained air-sacs.” In the adult bird these 
structures do appear as above described, but from working out 
the development, it is at.once clear that the cavity lying between 
the pulmonary aponeurosis and the oblique septum on each side, 
is not a division of the celom lined by peritoneum, but merely 
the cavities of the three posterior air-sacs, and therefore lined by 
endoderm. The dissepiments which are described as subdividing 
the subpulmonary chamber into loculi, are only the walls of the 
same air-sacs, which by the growth of the latter have become 
