Earliest Blood Vessels in Anterior Limb Buds. 305 



The effect of the intrusion of a nietameric influence in the plan 

 of the limb's vessels is as plainly marked in the case of its veins 

 as in the arteries, for of the row of venules entering the posterior 

 cardinal vein, those at segmental points are often definitely larger 

 than the remainder. Thus segmental veins as well as arteries exist. 



Fig. 11. — Croi-s section of iujected chick embryo of 34 somites in the region 

 of the anterior limb buds (embryo 10 of table), 



D. S. v., seventeenth dorsal Intersegmental vein. 



Sp. G., spinal ganglion ; N. Ch., uotochoi'd ; P. C. V., posterior cardinal vein ; 

 S. C. v., subcardinal vein ; U. V., umbilical vein ; D. S. A., seventeenth dorsal 

 intersegmental artery ( /. c, that of the eighteenth interspace) ; Subcl. Art., 

 subclavian artery ; N. \.. nephric vein. 



The fact that the veins draining more ventrally into the umbilical 

 vein are not effected by the segmental plan would indicate that a 

 metamerism does not pervade the entire limb tissue. One feels 

 that the segmental arrangement of the arteries and more dorsally 

 placed veins is the direct result of the influence of the adjoining 

 myotomes. 



I must comment here on the embrvo listed as J^o. 17 in the series. 



