6 4 



THE STUDY OF CHICK EMBRYOS 



Section through the Anlage of the Liver (Fig. 63). In this section the cavity of the 

 fore-gut is narrow, the gut being flattened from side to side. Ventrad there are evaginated 

 from the entoderm two elongate diverticula which form the anlages of the liver. On either 

 side of the anlages of the liver are sections of the vitelline veins on their way to the sinus 



Splanchnic mesoderm 



Ectoderm 



Posterior cardinal vei 

 Nolochori 



Somalopleurt 



Open gut 



Entoderm 



Chorion 



A mnion 

 Central canal 

 Spinal cord 



Mesodermal segment 

 R. descending aorta 



Ccdom 

 Somaiopleure 



FIG. 64. Transverse section through the cranial portion of the open intestine of a fifty-hour 



chick embryo. X 50. 



venosus at a higher level in the series. Note the intimate relation between the entodermal 

 epithelium of the liver and the endothelium of the vitelline veins. In later stages, as the 

 liver anlages branch, there is, as Minot aptly expresses it, "an intercrescence of the ento- 

 dermal cells constituting the liver and of the vascular endothelium" of the vitelline veins. 



Mesodermal segment 

 Descending aorta 

 Somatopleure 

 Somatic mesoderm 



Spinal cord 



Ectoderm 

 Notochord 



Somatic mesoacrm 



Splanchnopleitre^ / \ Splanchnic mesoderm 



Ccdom Entoderm 



FIG. 65. Transverse section through the seventeenth pair of mesodermal segments of a fifty- 

 hour chick embryo. X 50. 



Thus are formed the hepatic sinusoids of the portal system, which surround the cords of 

 hepatic cells. 



The septum transversum is still present at this level and lateral to the fore-gut are small 

 body cavities. Lateral to the body cavities appear branches of the posterior cardinal veins. 



