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TEXT-BOOK OF EMBRYOLOGY. 



appears. At the same time elevations appear between the succeeding depres- 

 sions, the first elevation appearing cranial to the first depression. (Compare 

 Figs. 122, 123.) The elevations are the branchial arches and the depressions are 

 the branchial grooves. Corresponding elevations and depressions also mark the 



Fig. 131. 



Fig. 132. 



Fig. 131. — Human embryo of 78 mm. (3 months). Minot, 

 Fig. 132. — Human embryo of 155 mm. (123 days). Minot. 



interior of the pharynx, so that the portions, of the wall of the pharynx which 

 correspond to the grooves are thin as compared with those portions which cor- 

 respond to the arches. 



The arches develop in order from the first to the fourth ; consequently they 

 are successively smaller from the first to the fourth (Fig. 122). The conditions 



