XIII 



PHYLUM CHORDATA 



411 



papillae make their appearance, arranged in narrow and well- 

 defined pterylse. 



At an early period capillaries appear in the extra-embryonic 

 blastoderm, between the opaque and pellucid areas, and give rise 



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

 am. cut edge of amnion ; an. anus ; an. ap. auditor y aperture ; an. s. auditory sac ; f. br. fore- 

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

 brain ; mn. mandibular arch ; na. nostril ; t. tail. (After Duval.) 



ar.i/asc 



FIG. 1015. Gallus bankiva. Egg with embryo and f ratal appendages, a. air-space ; all. 

 allantois ; am. amnion ; ar. rase, area vasculosa ; emb. embryo ; yk. yolk-sac. (After Duval.) 



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 



