EMBRYO OF SEVEN SEC 



this region, instead a diffuse network of mesoderm partly fills the space between 

 ectoderm, entoderm and mesothelium. This is termed mesenehyma and will 

 be described later. 



Neural plate Neural groove 



Ectoderm \ / .Mesodertnal segment 



Somatic, mesoderm \ jg^ / jfs^ / oe / on 



Splanchnic, mesoderm / \ ^\ Notochord 



Descending aorta ' ^ Entoderm 



FIG. 33. Transverse section through the fifth pair of mesodermal segments of a twenty-five-hour chick 



embryo. X 90. 



Mured crest: 

 Neural tube 



Ectoderm 

 Descending aorta. 



Efftbderm of Forty ut 

 Vltelline vein 



FIG. 34. Transverse section caudal to the fovea cardiaca of a twenty-five-hour chick embryo. X 90. 



Neural tube 



Ectoderm 

 Som. mesoderm 



*$* ffl* 1 

 Deseendintj aorta \lj; 



Splanchnic mesoderm 

 (Myocardium) 



Endolhehum of 

 heart lube 



Entoderm 



Splanchnic mesoderm j/ 

 FIG. 35. Transverse section through the fovea cardiaca of a twenty-five-hour chick embryo. X 90. 



Transverse Section through the Fovea Cardiaca (Fig. 35). This section is 

 marked by a vertical layer of the entoderm at the point where it is folded into 

 the head as the fore-gut. The entoderm is thickened laterally and forms a 

 continuous mass of tissue between the vitelline veins. The splanchnic mesoderm 



