464 MR. G. W. BUTLER ON THE SUBDIVISION OF [NoV. 19, 



side there is still a communication (*) between the hepatic and 

 post-hepatic parts of the abdominal cavity ; and comparing this with 

 figs. 1 5 & 17, which represent sections respectively dorsal and ventral 

 to the section in fig. 16, it will be seen that the more dorsal part of 

 the post-hejjatic septum is composed of the oblique abdominal septum 

 (y), while the more ventral part consists of the lateral "omental" 

 extension (/3). On the left side the ventral and dorsal components 

 of the post-hepatic septum never meet, and there is always in the 

 fowl a free communication between the " pulmohepatic recess " of 

 this side and the general intestinal cavity. In the duck this is 

 reduced to the condition of a small aperture (cf. supra, p. 454). 



With regard to the origin of this post-hepatic septum, it would 

 seem that the ventral portion (/3) is, so to speak, started by the 

 vitelline veins which cause considerable inward projections of the 

 lateral body-walls in which they run. With the closing-in of the 

 body-wall in the region of the umbilicus, the vessel of the left side 

 which alone continues as the allantoic vein (or in the adult as an 

 anterior abdominal vein carrying blood from the fat-laden omentum) 

 comes to assume a more central course, but the ventro-lateral attach- 

 ment of the membrane which supported these vessels persists. 



The dorsal component (y) of the post-hepatic septum, on the 

 other hand, is due to the extension laterally and posteriorly, by the 

 growth of the abdominal air-sacs, of the ridge that forms a backward 

 continuation of the pulmonary tissue of either side. And it is thus 

 that I believe that in those Sauropsida which have no similar arrange- 

 ment of air-sacs the post-hepatic septum, which may be present 

 (Crocodiles and Teiidse), is the homologue of the ventral component 

 of this septum in the bird — the dorsal part being merely repre- 

 sented by the membranous fold, which in many Lizards extends for 

 a considerable distance behind the lungs. 



IV. On the Body-cavity of the Lacertilia and of the 

 TeiidjE in particular. 



(a) The Lacertilia generally/. 



Turning now to the Lacertilia and recurring to the question of 

 the ventral attachment of the lungs. The left lung seems to have, 

 as a rule, its ventral border but slightly if at all attached, but there 

 is sometimes a short ligament connecting this with the liver or tissue 

 in front of that organ. 



The right lung, on the other hand, seems as a rule (cf. p. 465, 

 fig. A) to have its whole ventral border attached to the dorsal 

 wall of the right liver-lobe, or — seeing that dorsally it is attached 

 to the middle line by another ligament — it may sometimes be rather 

 described as set on the outer side of a membrane passing between 

 the right liver-lobe and the dorsal part of the median mesentery. 

 The spaces thus enclosed between the lung and its ligaments on the 

 outside, and the oesophagus and its ligaments in the middle line, are 

 homologous with the pulmohepatic recesses of birds above described 



