GERM LAYERS. 



71 



- Completion plate 



Embryonic disk 

 Hensen's node 



Primitive streak I Jl 



and groove 

 Embryonic disk 



'-v_ ! 



> Head process 



_ Prim. int. cord 

 - (protentoderm) 



r 



Ectoderm 



Volk entoderm 





- ■■ ■ - - •■ m - m ■:■■'■ ^Jti^^* 00 * 



-.— r-. - 



...» 





•®«** 





P T- I " 



Mesoderm 



S a 



Yolk entoderm 



Ectoderm 



Mesoderm 



■"■ ' ; ■■.'■•'■.■,;... 



Completion plate 



Medullary f 



Mesoderm 





'.5;'': ■: ... . • .-'■.'-• 



>, 



oik entoderm 



^JBMUi^.^ 





' 





S^&a^BSa 



Chordal plate (protentoderm) 

 Primitive groove 







Yolk entoderm 



**-«Jf.f 





Mesoderm 



Mesoderm 



Ss 



Post, end of prin 



streak 



- IV; •/;'/ 



.■:.'■'■' 





Mesoderm 



Fig. 54. — Surface view of embryonic disk of dog and transverse sections of same. Bonnet, 

 a, Disk somewhat further advanced than that in Fig. 53; the letters and figures (Si-S<) indicate planes 

 of sections in 6. m. gr., medullary groove. 



