198 THE DEVELOPMENT OF THE CHICK 



the atrium, the ventricular loop, and the bulbus arteriosus (Fig. 



^^^The truncus arteriosus lies in the floor of the pharynx and 

 gives off the following vessels: (1) a short branch, the external 

 carotid, extending into the mandibular arch; (2) complete arches 

 in the second, third, and fourth visceral arches which jom the 



Fig 115 - The circulation in the embryo and yolk-sac between the eightieth 

 and ninetieth hours of incubation, drawn from a photograph by A. H^ ^oie. 

 The arteries are represented in solid black; the veins in neutral tint, 

 fold of the yolk-sac covers the fore part of the head, 

 a. a. 2, 3, 4, Second, third, and fourth aortic arches ^o forta^ Ar , 



Atrium B a Bulbus arteriosus. Car. ext., External carotid. ^V,^;- 



Internal carotk . D. C, Duct of Cuvier. D. V., D^^^^us ^^^^^'^l./-' ^'^^y 

 W vein (anterior cardinal). 1. a. V., Left anterior vitelline ^^m 

 Posterior vitelline vein. S. V., Sinus venosus. V. c. p., Posterior caruii 

 veTn VenrVentricle. V. O. M. L., Left omphalomesenteric vein. 



