THE STUDY OF CHICK EMBRYOS 



Section through the Caudal End of the Heart (Fig. 46). The section passes through 

 the hind-brain. The descending aortae are separated only by a thin septum which is 

 ruptured in this section. The anterior cardinal veins are cut at the level where they bend 



Ectoderm 



Hind-brain 



Mesodermal segment 

 Anterior cardinal vein 

 Somatic mesoderm Ccelom 



Fore-gut 



Entoderm 



. . ^_^ ^ Splanchnic mesoderm 



Vitelline vein/ 



Heart Myocardium 



FIG. 46. Transverse section through the caudal end of the heart of a thirty-eight-hour chick 



embryo. X 75. 



ventrad to enter the heart. The mesothelial wall of the heart is continuous with the 

 splanchnic mesoderm. On the right side of the section there is apparent fusion between 

 the myocardium of the heart and the somatic mesoderm. A pair of primitive mesodermal 



Ectoderm 

 Mesodermal segment 



Neural tube 

 Notochord 



Somatopleure 



Extra-embryonic ccelom 

 Entoderm 

 Right vitelline vein Sp i a ' nchnic | 'W viteUine vein 



mesoderm Entoderm Fore-gut 



FIG. 47. Transverse section through the intestinal portal of a thirty-eight-hour chick embryo. 



X 90. 



segments may be seen in this section lateral to the hind-brain. It may be noted here that 

 the primitive segments were not present in the sections of the head previously studied. 

 Section through the Intestinal Portal (Fig. 47) . The descending aortce now form a single 

 vessel, the dorsal aorta, the medium septum having disappeared. The section passes through 

 the entoderm at the point where it is folded dorsad and cephalad into the head as the fore- 



