No. i.] 



THE LESSER PERITONEAL CAVITY. 



167 



of Paris, from which the metal and wax are to be removed 

 by boiling. The mould is now to be filled with lead or solder, 

 and the plaster broken off. By this method any portion of an 

 embryo can be modelled in lead or solder. The method does 

 not cost as much labor as Born's, and in many respects exceeds 

 it in usefulness. 



Birds. 



Shortly after the heart is formed, the head begins to flex 

 upon the body, and the pharyngeal entoderm is pushed at first 

 to the dorsal side of the heart, and 

 then into the branchial region. At 

 the time this peculiar rotation is tak- 

 ing place, the sinus venosus holds 

 quite a stationary position, while the 

 heart is thrown over to its ventral 

 and aboral side. At this time a single 

 omphalo-mesenteric vein empties into 

 the heart, and from either side an ad- 

 ditional branch, the ductus Cuvieri, is 

 added. The pleuro-peritoneal cavity 

 now breaks through on the aboral side 

 of the ductus, thus causing the vessel 

 to perforate the pleuro-peritoneal cav- 

 ity (Fig. 1), as described by Balfour. 1 

 The union of the cavities across the 

 median line now extends more aboral- 

 wards, and then communicates with 

 the false amnion. After we have 

 arrived at this stage, the mesentery 

 is fully formed, the cavities on either 

 side communicating across the median 

 line only in the neighborhood of the 

 heart. The pulmonary buds are form- 

 ing, and the alimentary canal is almost 

 completely closed. Just at this time 

 two sacs, one on either side, are formed 

 from the splanchnic wall of the pleuro- 



Fig. 1. Section through the 

 region of the heart of a chick of 

 70 hours. Enlarged 50 times. 

 The section strikes the oral end 

 of the gastric diverticulum, G. D., 

 anil the tips of the pulmonary 

 buds, L. A few sections deeper 

 the gastric diverticula communi- 

 cate with the pleuro-peritoneal 

 cavity. //., heart; D. C, ductus 

 Cuvieri; B. A., bulbus aortce. 



1 Comparative Embryology, Vol. II, p. 627, Fig. 352. See also His, Hiinschen 

 Afonograph.fT^. XI, Figs. I, 12, 13, 14; Duval, Planche. XXII, Figs. 358, 359, 360 : 

 PI. XXV, Figs. 403-407. 



