THE EODY-CAVITIES 



339 



tension of the pleural cavities ventrally that splits the mem- 

 branous pericardium from the body-wall. 



Derivatives of the Septum Transversum. From the preceding 

 account it will be seen that the following are derivatives of the 

 septum transversum: (1) The posterior part of the pericardial 

 membrane. (2) The pleuro-pericardial membrane. (3) The liver 

 with its vessels and gastro-hepatic and primary ventral ligaments. 



Fig. 194. — Photograph of a transverse section of an 8-day chick. 



abd. A. S., Abdominal air-sac. A. coel., Coeliac artery. Ao., Aorta. 

 A. o. m., Omphalomesenteric artery. Aiir. d., Right auricle. Cav. pc, 

 Pericardial cavity. M. D., Miillerian duct. M. pc, Membranous pericar- 

 dium. Msn., Mesonephros. Pr'v., Proventriculus. S., Septum ventricu- 

 lorum. V. c. i., Vena cava inferior. V. h. d., Right hepatic vein. V. d., 

 Right ventricle. V. s., Left ventricle. 



(4) A small part of the heart (the sinus venosus). As regards 

 the last, it should be noted that the anterior portion of the original 

 septum transversum is gradually constricted from the major 

 posterior portion and becomes established as the sinus venosus; 



