136 



THE DEVELOPMENT OF THE CHICK 



O-J7. 



Telenc 



-A.o.m. 



prstr 



FIG. 73. Entire embryo of 20 s, viewed 

 as a transparent object from above. 

 The cranial flexure and the rotation of 

 the head of the embryo have made 

 considerable progress. 

 A. o. m., Omphalo-mesenteric artery. 

 Cr. Fl., Cranial flexure. D. C., Duct of 

 Cuvier. Dienc., Diencephalon. Mesenc., 

 Mesencephalon. Metenc., Metencepha- 

 lon. Myelenc. 1, and 2, Anterior and 

 posterior divisions of the myelencepha- 

 lon. Telenc., Telencephalon. Vel. tr., 

 Velum transversum. Other abbrevia- 

 tions as before, x 30. 



cent to arid surrounding the embryo, and a choriogenous zone, 

 comprising the remainder. 



The method of formation of amnion and chorion is as follows: 



