-227 



7,50 



FIG. 45. SAGITTAL (MEDIAN - LONGITUDINAL) SECTION OF AN 

 EMBRYO OF 26 HOURS. (After Duval.) 



A, anterior end of head. CM, medullary canal. EC, endothelium of heart. 

 RE, limit of head-fold, ex, ectoderm, in, entoderm. PC, pericardium. /%, 

 pharynx or fore-gut. Vi, fore-brain, b, mesoderm. 



133 



