454 MR. G. W. BUTLER ON THE SUBDIVISION OF [NoV. 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 

 (h, 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 to them. The ligaments referred to may 

 be called the pulmohepatic ligaments (a, a). I now call special 

 attention to them because in tlie 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, 4G, 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 {h, 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 Fov\l, 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 «ill call i\\e 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 

 antcrieure of Milne-Edwards), and oblique septum (for the plan 

 oblique or diaphragme thoraco-abdominal of Sappey, diaphragmice 

 posterieure 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 oiseauxla cavite abdominale en deux cavites plus petites, 

 I'une anterieuie, qui represente I'abdomen et qui loge le foie, I'autre posterieure, 

 qui represente le bassin et qui loge I'estomac et les intestines ; cette cloison 

 fibreuse extremeuient remarquable dans I'autricbe ou elle a ete decrite par 

 Perrault sous le nom de diaphragme transversal, s'inserea toute la circonfereuce 

 des OS du bassin, et soutient I'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. 



