156 THE DEVELOPMENT OF THE CHICK 
pienc. 
Mesenc.  / Waren 
— 
Sy Zelenc 
FL = 
Metenc. f= —Op. Ves. 
Myelenc./ 
au. P ae Ni Ph. 
Myelenc.2.“* DiC. 
5.2.- 4 
\ 
Pr str <=" 
Fic. 73. — Entire embryo of 20s, 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. Diene., Diencephalon. Mesenc., 
Mesencephalon. Metene., Metencepha- 
lon. Myelene. 1, and 2, Anterior and 
posterior divisions of the myelencepha- 
lon. Telene., Telencephalon. Vel. tr., 
Velum transversum. Other abbrevia- 
tions as before. x 30. 
cent to and surrounding the embryo, and a choriogenous zone, 
comprising the remainder. 
The method of formation of amnion and chorion is as follows: 
