Development of the Third Day 197 



rated. The thumbs should, at first, be closely 

 pressed against the forefingers, and should be 

 considered as fused with them. If the fingers 

 and hands are slightly bent, there will be a 

 space between the two hands that may be 

 taken to represent the pharnyx of the chick, 

 while the four fingers will represent the first 

 four gill arches, and the spaces between the 

 fingers will represent the first three gill clefts. 

 The closure of the visceral clefts may be 

 represented by bringing the fingers of each 

 hand together. The forefingers, which should, 

 in reality, be the only ones which actually 

 meet in the mid-ventral line, will represent the 

 mandibular arch, forming the lower half of the 

 mouth. The formation of the maxillary arch, 

 by processes budded out from the upper ends 

 of the mandibular arch, may be represented 

 by separating the thumbs from the fore- 

 fingers, and pointing them towards each 

 other, without letting them come in con- 

 tact ; the triangular space between the thumbs, 

 thus held, being filled, in the imagination, by 

 the fronto-nasal process. The angles between 

 the thumbs and the forefingers will repre- 

 sent the angles of the mouth. Of course, to 

 make the comparison more striking, there 



