454 MR. G. W. BUTLER ON THE SUBDIVISION OF [Noy. 19, 
of this latter septum enters into the dorsal wall of the sacs in ques- 
tion, for the anterior portion of this wall is formed by the liver-lobes 
(A, h') themselves, and by the ligaments (a, a) which pass from the 
liver to the more vertical portions of the ‘‘ oblique septum.” The 
lines of attachment of these ligaments to the oblique septum follow 
approximately the ventro-external margins of the lungs, where this 
latter membrane is apposed tothem. The ligaments referred to may 
be called the pulmohepatic ligaments (a, a). I now call special 
attention to them because in the sequel I use them as a landmark 
in comparing the different types. 
On cutting through the pulmohepatic ligament there is exposed, 
on the right side, another entirely closed sac (Plate XLIX. figs. 44, 
45, 46, 2), bounded externally by the more vertical portion of the 
‘oblique septum,” dorsally by the septum (y) above referred to, 
and in part by the more horizontal portion of the “ oblique septum.” 
The right liver-lobe (A, figs. 44 & 46) is attached to the dorsal wall 
of this sac from the point where the vena cava inferior, enters it, 
backwards, and the sac is thus partially subdivided into two. 
In the Duck, the corresponding sac of the left side appears to be 
quite closed; but it really communicates with the post-hepatic or 
intestinal portion of the body-cavity by a small aperture, which is 
merely closed by the left ‘‘ abdominal”’ air-sac flapping against it. 
In the Fowl, however, the continuity of this sac with the intestinal 
cavity is plain, its hinder end being freely open. 
These two sacs in the Bird, which are partly bounded by the 
pulmohepatic ligaments ventro-laterally, I will call the pulmohepatic 
recesses, and their homologies will be referred to later (p. 460, 
§ III.c). For a capital description of the avian diaphragm reference 
may be made to Sappey (1, pp. 21—26), also to the ‘ Comparative Phy- 
siology ’ of Milne-Edwards (vol. ii. p. 401) and to Huxley (4). All 
three accounts accord perfectly. Milne-Edwards’s, in fact, differs 
little from Sappey’s, even in nomenclature. Huxley introduces 
a few new terms, such as pulmonary aponeurosis (for the plan 
transversal or diaphragme pulmonaire of Sappey, the diaphragmite 
antérieure of Milne-Edwards), and oblique septum (for the plan 
oblique or diaphragme thoraco-abdominal of Sappey, diaphragmite 
postérieure of Milne-Edwards). I here use Huxley’s terms for these 
two parts of the diaphragm. I assume that the general relations 
of these two membranes and their air-sacs, which he and Sappey 
have so clearly described, require no explanation on my part. 
Sappey makes it very clear that he regards the two membranes 
the abdominal air-sacs, “ En bas et en avant ils s’'appuient sur une cloison fibreuse 
qui divise chez tous les oiseaux la cavité abdominale en deux cavités plus petites, 
Pune antérieure, qui représente l’abdomen et qui loge le foie, autre postérieure, 
qui représente le bassin et qui loge l’estomac et les intestines; cette cloison 
fibreuse extrémement remarquable dans l’autriche ot elle a été décrite par 
Perrault sous le nom de diaphragme transversal, s'insére 4 toute la circonference 
des os du bassin, et soutient l'estomac ainsi que le tube intestinal.” 
It will be noted that the two sacs I am describing form only the ventral 
portion of the anterior cavity of which Sappey here speaks. 
