THE ELASMOBRANCH FISHES 



177 



separated from the anterior efferent-collector dorsally, and its blood readies 

 the anterior efferent-collector in front of it only by means of cross-trunks 

 {dr., figs. 162 and 165). It is by means of such cross-trunks that the last 

 efferent-collector is relieved of its blood. In fact, the posterior collector of 



Fig. 166. Hypobranchial arteries. A. Mustelus antarcticus. (From T. J. Parker.) B. Mus- 

 telus canis. (From Ferguson.) 



O.Z., anterior lateral (lateral abdominal) artery; hr.a., brachial artery; hr.af}'*, first and 

 fourth branchial afferent arteries; co.a., coracoid artery; cm., commissural artery; cr.l., left 

 coronary artery; cr.p.. posterior coronary; e.c, external carotid; hy.af., hyoidean aifereut; 

 l.lil)., lateral hypobranchial; m.a., mandibular artery; m.hb., median hypobranchial ; n.a., 

 nutrient artery; pc, pericardial; s.cl., subclavian; v.a., ventral aorta; III, position of 

 third gill cleft. 



each gill empties a considerable amount of its blood into the anterior effer- 

 ent-collector of its own gill by similar cross-trunks. These trunks may be 

 numerous as in Heptanchus maculatus, few as in Squalus, or they may be 

 single as in Dasyatis {dr., fig. 162). 



The circuits made by the efferent-collectors, as we have said, are drained 

 into the dorsal aorta by means of the efferent arteries. These arteries we shall 

 consider after discussing certain branches given off by the efferent-collectors. 



