310 • Herbert 31. Evans. 



There are six subclavians on either side in this embryo. The 

 first subclavian on the right side occurs midway between the six- 

 teenth and seventeenth dorsal segmental vessels, the second subcla- 

 vian opposite the seventeenth segmentals, the third somewhat beyond 

 this point, the fourth just in front of the eighteenth dorsal segmen- 

 tals, the fifth somewhat beyond this point, and the sixth midway 

 between the eighteenth and nineteenth see-mentals. 



SpCh- 



FiG. 15.— Cross section of the duck einliryo shown in Fig. 14 in the region 

 of the anterior limb buds. One notes the midlateral origin of the subclavian 

 capillaries from the aortic wall. 



On the left side, the first subclavian arises opposite the seven- 

 teenth segmental vessels, the second midway between these and the 

 eighteenth vessels, the third just in front of the eighteenth seg- 

 mentals, the fourth midway between the eighteenth and nineteenth 

 segmentals, the fifth at the level of the nineteenth segmentals, and 

 the sixth midway between the nineteenth and twentieth segmen- 

 tals. 



It is impossible, here also, to see in the arrangement of the sub- 

 clavians any influence of metamerism. There are as many vessels 

 out of segmental alignment as are in accordance with it and this 

 because, again, in the origin of the typical plexus here as many 



