DEVELOPMENT OF THE LESSER PERITONEAL 

 CAVITY IN BIRDS AND MAMMALS. 



F. MALL. 



The excellent posthumous paper of Budge, 1 although incom- 

 plete, adds a great deal to our knowledge of the early formation 

 of the pleuro-peritoneal cavity. By means of injection he filled 

 the spaces which first appear in the chick with an aqueous 

 solution of Prussian blue. By this method he filled the various 

 spaces forming the ccelom as they appeared, and found that they 

 were intimately connected with the lymphatics. 



The vascular layer formed between the splanchnopleur and 

 entoderm in birds is too well known to allow further descrip- 

 tion. According to Budge, it may be split into two layers, — a 

 dorsal or lymphatic, and a ventral or vascular. As the first 

 blood-vessels are formed, lymph spaces appear on their dorsal 

 side, which flow together to form networks, and accompany the 

 primitive veins to the axial part of the germinal area. Here the 

 lymphatics form two spaces, one on either side of the body, 

 which are soon, connected by a bridge and thus form an H. 

 The cross-piece of the H lies oral to the sinus venosus which 

 has just been formed. 2 In its further development the sinus 

 grows to the dorsal side of the cross-piece, thus reversing the 

 relation of the vascular to the lymphatic system. The uprights 

 of the H fall to the outside of the body, and are swallowed up 

 in the formation of the false amnion. The cross-piece forms 

 mainly the pericardial cavity. Shortly before the heart is 

 formed, two diverticula grow from the cross-piece, one on either 

 side of the chorda, towards the tail of the body, forming the 

 primitive pleuro-peritoneal cavities. By later anastomoses, and 



1 Budge, His u. Braune's Arc/iiv, 1889. 



2 Duval, Atlas de Embryologie, Paris, 1889, gives on PI. XVIII, 289 to 292, sec- 

 tions through the heart region before the cross-piece of the II is formed. On PI. 

 XX, Fig. 319, and PI. XXI, Figs. 338, 339 to 340, the coelomic cavities communicate 

 on the ventral side of the heart. 



165 



