DEVELOPMENT OF THE SPINAL COLUMN. 

 FIG. 265. 



673 



Transverse section through the dorsal region of an embryo chick of forty-five hours. 

 (Foster and Balfour.) A. Epiblast. M.c. Medullary canal. P.v. Proto vertebrae. W.d. 

 Wolffian duct. p.p. Pleuroperitoneal cavity. So. Sornatopleure. S.p. Splanchnopleure. 

 v.v. Vessels, o.o. Aorta. B. Mesoblast. C. Hypoblast. o.p. Line of union of opaque 

 and pellucid areas, w. Spheres of the white yelk. 

 67 



