Chap. X.] 



THE HEART AND CIRCULATION. 



197 



and slightly in front of the sinus venosus is the auricle (au.), 

 through which all the blood passes on its way to the thick-walled 

 ventricle (v.). From the ventricle it passes into the thick-walled 

 bulbils arteriosus (b. a.), and thence to the ventral aorta (v. ao.). 

 Note that there is one undivided auricle and one undivided 

 ventricle. 



.Vtt. ep.W. ef.tr.a. ac v 



af.lr.7T 



v. 



FIG. 59. DIAGRAM OF HEART AND GREAT VESSELS OF COD-FISH. 

 a. c. v. Anterior cardinal vein. a. p. Artery supplying pelvic fins. af. br. a. 

 Afferent branchial arteries, au. Atrium or auricle. &. a. Bulbus arteriosus. 

 car. Carotid artery, cce. a. Caeliac artery, d. ao. Dorsal aorta, d. c. Ductus 

 Cuvieri. ef. "br. a. Efferent branchial arteries, ep. br. a. Epibranchial artery. 

 he. v. Hepatic vein. hy. Hyoidean artery, i. j. v. Inferior jugular vein. 

 me. a. Mesenteric artery, p. c. v. Posterior cardinal vein. ps. Pseudo- 

 branchia on inner surface of operculum. s. a. Subclavian artery, s. v. Sinus 

 venosus. sp. v. Spermatic vein. tr. Transverse vessel completing circulus 

 cephalicus. v. a. Ventral aorta, v. Ventricle. 



The arrangement of the great vessels is shown diagrammatic- 

 ally in Fig. 59. The ventral aorta (v. ao.) gives off on either 

 side four afferent branchial arteries (af. br. a.) to the four complete 

 gills. From the gills there pass on each side four efferent bran- 

 chial arteries (ef. br. a.), which open into a vessel (epibranchial 

 artery ', ep. br. a.), running along the dorsal ends of the gill arches. 

 Traced forwards the epibranchials give off the carotid arteries, 

 and curving round unite to complete the circulus cephalicus. 

 Traced backwards the epibranchials unite posteriorly to 



