EMBRYO OF TWENTY-SEVEN SEGMENTS 



septum transversum (anlage of diaphragm) in which the common cardinal veins cross to the 

 sinus venosus. 



Spinal cord 

 Mesodermal segment 



Dorsal aorta 

 Mesenchyme 



Common cardinal vein 



Entoderm 

 Myocardium 



Atrium 

 Endothelium of heart 



FIG. 62. Transverse section through the sinus venosus and common cardinal veins of a 

 fifty-hour chick embryo. X 50. 



Fore-gut 

 L. vitelline vein 



Splanchnic mesoderm 



Posterior cardinal vein 



Splanchnic mesoderm 

 Liver anlage 



Vitelline vein 



FIG. 63. Transverse section through the anlage of the liver of a fifty-hour chick embryo. 



X 50. 



The somatopleuric folds of the amnion envelop the right side of the embryo, and the 

 ectoderm of these folds now forms the outer layer of the chorion and the inner layer of the 

 amnion. The mesodermal components of the folds have not yet united. 



