FROM TWELVE TO THIRTY-SIX SOMITES 



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Fig. 99. — Entire embryo of 31 somites viewed as a 

 transparent object, 

 am. Umb., Amniotic umbilicus. B. a., Bulbus 

 arteriosus, cerv. Fl., Cervical flexure, ch. Fis., Cho- 

 roid fissure, cr. Fl., Cranial flexure. D. C, Duct of 

 Cuvier. ex. o. c, External layer of the optic cup. 

 int. o. c, Internal layer of the optic cup (retina.) 

 N'm., Neuromere of myelencephalon. olf., Olfactory 

 pit pc. W., Line of attachment of amnion to peri- 

 cardial wall. V. C. 1, 2, 3, First, second, and third 

 visceral clefts. Other abbreviations as before. 



