Fig. 8. — Chick embyro of 38 somites (embryo 17 of table) showing multiple 

 siibclavians and their relation to the dorsal segmental vessels, x 53i/4. 



5th Dor. Seg. Ves., tifth dorsal segmental vessels, occupying the sixth inter- 

 somitic septum. 



Ot. Ves., otic vesicle. 



4th Subcl. Art., fourth subclavian artery of right side, opposite the seven- 

 teenth dorsal segmental vessels (those of the eighteenth septum) and hence 

 likely to become the chief primary subclavian artery of later stages. 



U. v., umbilical vein, here subserving no function other than draining the 

 limb bud. 



The figure shows clearly the dorsal segmental vessels and their distribution 

 as a simple capillary plexus investing the lateral walls of the spinal cord. 



