CHORDATA. 



337 



of the heart. The main trunk leaving the heart is called the 

 aorta. As the vessels are followed from the heart they branch 

 and become smaller and the walls become thinner. The final 

 divisions are the capillaries through the thin walls of which 



FIG. 164. 



FIG. 165. 



. v. r. 



a. a. 



l-c. v. I. 



c. v. I. 



p.c. 



FIG. 164. Diagram of the heart, the branchial arches, and the principal veins in the 

 Teleosts. Ventral view. The heart is represented without the sigmoid flexure; that is, 

 with the auricle posterior. The same is true of Figs. 165 to 169. a, aorta; au., auricle; 

 br.a., branchial arches of the aorta (1-4, numbering from the front); c, carotid; c.v., 

 cardinal veins (right and left); d.a., dorsal arteries; ;', jugular veins; d.c., ductus 

 Cuvieri; s.i'., sinus venosus; i', ventricle. 



Questions on the figure. Refer to the table on page 340 and identify 

 the parts there described. Compare this figure with those following 

 (Figs. 165-169). Compare also with Figs. 178 and 179, Ch. XX. Which 

 is the anterior and which the posterior portion of this and the follow- 

 ing figures ? 



FIG. 165. Diagram of heart and branchial arches in Ceratodus (one of the Dipnoi). 

 Position and lettering as in Fig. 164. a.b., air bladder (lung); p. a., pulmonary artery; 

 p.c., post caval vein (right) ; p.v., pulmonary vein. 



Questions on the figure. What organs appear in this diagram which 

 are not present in Fig. 164? What changes of the various portions do you 

 note in comparing the two figures? 



23 



