The Ark 



Fig. 49. Reconstruction of human emljryo of aljout 17 days 

 (His): ov, optic vesicle, ot, otic vesicle: no, uc', notochord ; 

 hdg, head <(ut : \-s, vitelline sac; 1, li\'er : v, ta, primitive ven- 

 tricle and truncus arteriosus; va and da, ventral and dor.sal 

 aorta; ; aa, aortic arches ; jv, primitive juglar vein ; cv, cardinal 

 vein ; dC, duct of Cu\'ier ; u\",ua, umbilical vein and artery ; al, 

 allantois ; uc, umbilical cord. iHeisler). 



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