198 THE DEVELOPMENT OF THE CHICK 
the atrium, the ventricular loop, and the bulbus arteriosus (Fig. 
116). 
The truncus arteriosus les 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 
elas taen Wee 
Via. 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., Duetus venosus. J., Jugu- 
lar vein (anterior cardinal). 1. a. V., Left anterior vitelline vein. p. V., 
Posterior vitelline vein. S. V., Sinus venosus. V. e. p., Posterior cardinal 
vein. Ven., Ventricle. V.O.M. L., Left omphalomesenteric vein. 
