198 



THE DEVELOPMENT OF THE CHICK 



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

 116). 



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 join 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. Cole. 

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

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

 a. a. 2, .3, 4, Second, third, and fourth aortic arches. Ao., Aorta. Atr., 

 Atrium. B. a., Bulbus arteriosus. Car. ext., External carotid. Car. int., 

 Internal carotid. D. C, Duct 'of Cuvier. D. V., Ductus venosus. J., Jugu- 

 lar vein (anterior cardinal). 1. a. V., Left anterior vitelHne vein. p. V., 

 Posterior vitelHne vein. S. V., Sinus venosus. V. c. p.. Posterior cardinal 

 vein. Ven., Ventricle. V. O. M. L., Left omphalomesenteric vein. 



