1889.] THE BODY-CAVITY IN LIZARDS, ETC. 463 



the chick are fairly similar, and (p. 214) giving the resume from 

 which a quotation has already been made (p. 459). 



III. (e). On the Development of the two Parts of the Post- 

 hepatic Septum of the Bird. 



We have now to refer to the developmental changes grouped 

 under heads B & C (p. 456). 



First, with regard to the development of the " oblicpie abdominal 

 septum." 



Ravn {op. cit, p. 140) calls by the name of " vena-cava-falte " or 

 " plica venae cavse " the ridge that occurs in Mammals as a backward 

 continuation of the embr^vonic lung-substance, because through it 

 the vena cava inferior passes on its way from the kidneys to the liver 

 and heart. But it will be seen on reference to the Plates, figs. 5 & 6, 

 which together with fig. 7 show three sections of a chick of 7th day \ 

 that there is a horizontal ridge of the same nature on the left side 

 also (y, y), where of course there is no vena cava inferior. 



Later stages in the development of this septum are shown in the 

 series of transverse sections of embryo of 10th day (figs. 20, 21, 

 -2, 7, y), and in the transverse sections of 12th day (figs. 27 & 28, 



y> y)- 



It will be seen that the growth of the abdominal air-sacs has 

 considerable influence on the development of this septum, into which 

 they extend from its outer anterior border. We may say in fact 

 that though a starting-point is supplied by the ridge (y) which is 

 visible as a backward continuation of the pulmonary mesoblast in 

 the earliest stages, it is only when the abdominal air-sacs have 

 attained some degree of development (as at about the time of the 

 completion of the avian diaphragm, 9th to 1 0th days), that a true 

 septum reaching from the lateral walls to the median vertical 

 mesentery (c/l fig. 22, y, y) is apparent and begins to extend 

 posteriorly and obliquely ventralwards. 



This oblique abdominal septum, or anterior and dorsal portion of 

 the post-hepatic septum, is shown in its adult relations in figures 45 

 and 46, y, y (transverse sections). 



The ventral part of the latter is formed by the laterally extended 

 ventral ligament of the gizzard and hinder part of liver, which goes 

 by the names of gastrohepatic ligament and the great omentum. 



We see this membrane in the longitudinal-vertical section of 10th 

 day (taken to the right of the middle line, wherefore the gizzard 

 does not appear) (fig. 18, /3) extending from the ventral body-wall 

 to the posterior side of the liver. It is shown also in figs. 13, 17, 

 19, 20, 26, 27, 28, and also in 29, /8, fl. Further, I would call 

 attention to fig. 16, which is a longitudinal-horizontal section through 

 the more dorsal part of the gall-bladder (b.g) and the antero-ventral 

 corner of the lung (pul.) of a chick of the 12th day. On the right 



^ Owing to the curvature of the embryo at that date, these are partly horizontal- 

 longitudinal and partly transverse. They are very similar to figures 581 and 

 582 in Duval's Atlas ; but the latter fail to show the presence of the ridge y 

 on the left side. 



