1889. | THE BODY-CAVITY IN LIZARDS, ETC. 455 
referred to, between which lie the two pairs of air-sacs that he calls 
réservoirs diaphragmatiques or moyens (intermediate air-sacs of 
Huxley), as constituting a single diaphragm ; and Milne-Edwards 
says (/oc. cit.), “’appareil diaphragmatique des oiseaux se compose 
de deux portions ou diaphragmites.” This unity of the whole 
apparatus, which is very apparent when the development is followed 
(¢f. § IIT.), cannot, I think, be too clearly kept in view, especially 
when homologies are being discussed. 
In this paper I refer to all from the anterior or dorsal face of the 
pulmonary aponeurosis to the peritoneum covering the posterior or 
ventral face of the oblique septum, as the dvian diaphragm, in con- 
tradistinction to the Mammalian diaphragm, with which, in agree- 
ment with Huxley’s verdict, it is argued in the sequel it has little, 
if any, true homology. 
With regard to the term “ oblique septum” of Huxley. As he 
speaks (p. 562) of the four post-bronchial air-sacs of either side as 
being shut off by the “oblique septum” in a similar kind of way, I 
presume that he includes under this term the septum (y in the 
Plates) dorsal to the liver, above referred to. At all events in using 
this term, I refer merely to that septum which in the Fowl is (cf. 
p. 458), so to speak, blown away from the other part of the Avian dia- 
phragm by the growth of the intermediate, or diaphragmatic, air-sacs. 
I would call this septum (y), which on either side forms the 
dorsal wall of the pulmohepatic recess, and into which a large part 
of the abdominal air-sac projects’, the oblique abdominal septum. 
It is true that the more lateral parts of this septum, in that they 
take their final form in connexion with the abdominal air-sac, might 
so far be held to resemble the “ oblique septum ” proper, in its 
relation to the diaphragmatic air-sac ; but this would not apply to the 
more median parts of the septum (y), and the nature of the two things 
is really very different. That which I have termed the oblique abdo- 
minal septum does really separate one part of the body-cavity from 
another, as described bySappey(footnote, p. 454 above), and is covered 
on both sides by peritoneum ; but the “ oblique septum ”’ is only part 
of a coelomic septum, the otier part being the pulmonary apo- 
neurosis. 
The oblique abdominal septum we might perhaps regard as a 
backward continuation of the whole avian diaphragm with the abdo- 
minal air-sacs between its dorsal and ventral laminee, just as the 
intermediate or diaphragmatic air-sacs lie between the two laminw of 
the latter. 
III. On rae Devetopment anp Homoxocties OF THE 
VARIOUS SEPTA IN THE Bopy-Cavity OF THE CHICK. 
We may now turn to consider the development of the septa in 
the body-cavity of the Fowl, to which reference has been made in 
the preceding section. 
1 Sappey (see footnote, p. 454) says that these air-sacs rest on (s’appuient 
sur) the septum in question; but it is more correct to say that they project into 
it, in the end, as it were, blowing away a dorsal lamina from the rest, 
