Earliest BJoocl Vessels in Anterior Limb Buds. 



207 



on these occurrences, to call them "unusual divisions" and "island 

 formation," etc., yet this is all to be expected of capillaries tending 

 to plexify.'^ It is, indeed, more remarkable that the subclavian 

 capillaries usually cross the posterior cardinal vein before anasto- 

 mosing to any great extent. The general appearances given by the 

 limb vessels in these two embryos are quite significant. They must 



Post Card. 

 Vzin. 



-I9V>D.I.V 



Fig. 6. — Right wing bud of cbicl^ embryo of 31 somites (embryo 5 of table), 

 showing primary subclavian capillary plexus, x ^^V-z- Instances of "insel- 

 bildung" and early division of the subclavians are seen. 



19th D. I. v., nineteenth dorsal intersegmental vein (that of the twentieth 

 interspace). 



convince one of the existence here of a simple plexus — a plexus 

 the first meshes of which are elongated, as a rule, but a true plexus, 

 nevertheless, of true capillary vessels. Nor would any of the appear,- 

 ances lead one to believe that this primitive plexus in the limb is 

 in any way arranged according to a segmental plan. 



I have designated Embryo Y as the last of those having the sub- 



^hus Rabl seems surprised at these appearances. "Die mittlere der drei 

 Subclavien zeigt eine besoudere Eigeutiimlichkeit, indem sie sich unmittelbar 

 nach ihrem Ursprung teilt." P. 355, loc. cit. See also his text figures. 



