XIII 



PHYLUM CHORDATA 



411 



papillae make their appearance, arranged in narrow and well- 

 defined pterylae. 



At an early period capillaries appear in the extra-embryonic 

 blastoderm between the opaque and pellucid areas, and give rise 



_J . 



cm. 



TIG. 1014. Gallus bankiva. Two stages in the development of the embryo, all. allantois ; 

 am. cut edge of amiiion ; an. anus ; au. af>. auditory aperture ; au.s. auditoiy sac ; f. br. fore- 

 brain ; /. 1. fore-limb ; h. br. hind-brain ; It. I. hind-limb ; lit. heart ; /<. hyoid arch ; i. b. mid- 

 brain ; 'm, i. mandibular arch ; na. nostril ; f.^tail. (After Duval.) 



all 



TIG. 1015. Gallus bankiva. Egg with embryo and fcetal appendages. </. air-space ; all. 

 allant'ds ; //<. amnioii ; a;-, rase, area vasculosa; ciu/j. embryo; v'/,-. yolk-sac. (After Dural.) 



to a well-defined area vasculosa (Fig. 1015, ar. vase.) : they are sup- 

 plied by -vitelline arteries from -the dorsal aorta, and their blood is 

 returned by vitelline veins which join the portal vein and take the 



