CHORDATA 



339 



divisions are the capillaries through the thin walls of which 

 the blood exchanges materials with the tissues (Fig. 34, c.s.; 

 c.r.). The capillaries unite to form the smaller veins and these 



FIG. 1 66. 



FIG. 167. 



c. v. r._ 



c. v. I. 



FIG. 166. 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. 167 to 170. a, aorta; au., auricle; 6r.o., branchial arches of the 

 aorta (1-4, numbering from the front); c, carotid; c.v., cardinal veins (right and left); d.a., dorsal 

 arteries; j, jugular veins; d.c., ductus Cuvieri; s.v., sinus venosus; v, ventricle. Only four arterial 

 arches are shown. 



Questions on the figure. Refer to the table on page 343 and identify the parts 

 there described. Compare this figure with those following (Figs. 167-171). 

 Compare also with Figs. 181 and 182, Ch. XX. Which is the anterior and which 

 the posterior portion of this and the following figures? 



FIG. 167. Diagram of heart and branchial arches in Ceratodus (one of the Dipnoi). Position 

 and lettering as in Fig. 166. 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. 166? What changes of the various portions do you note in com- 

 paring the two figures? 



uniting, complete the circuit back to the heart. It is evident 

 that the capillaries are the most important portion of the 

 system, the part for which the rest in reality exists. 



