162 



THE ELASMOBRANCH FISHES 



fig". 151) , and another, the one behind the cleft. These two arteries, the first and 

 second efferent-collectors, unite both ventrally and dorsally, forming a loop 

 around the cleft (fig. 151). The third and fourth efferent-collectors encircle 

 the second pocket as the first and second encircle the first pocket, but the one 

 forming the anterior part of the loop, which is the posterior efferent-collector 

 of the first holobranch, is small and has an irregular course. As it passes veu- 



Fig. 151. Efferent-collector arteries, Eeptanchus maculatus. (R. T. Trotter, orig.) 



br.ef.^'^, first and sixth branchial eiJerent arteries; cm.^'^, second and sixth commissural 

 arteries; c.tr., cross-trunk; d.a., dorsal aorta; e.c, external carotid; efc}'^, first and thir- 

 teenth efferent-collector arteries; hy.ef., hyoidean efferent; ps., pseudobranchial artery; 

 th., posterior thyroid artery. 



trally it may increase somewhat in size and is connected with the efferent- 

 collector in front of it by numerous cross-trunks. Ventrally it joins the larger 

 efferent-collector behind the cleft, the anterior efferent-collector of the second 

 holobranch, and dorsally it loops back also making connection with the same 

 vessel. Similar efferent-collectors encircle the remaining pockets, except the 

 last, where a complete loop is not formed due to the lack of gill filaments on 

 the posterior wall of the pocket. The blood from the last (thirteenth) efferent- 

 collector is drained by means of cross-trunks {c.tr.) into the twelfth efferent- 

 collector through the greater part of the holobranch; and ventrally the last 

 efferent-collector joins the one in front of it directly. 



Branches of Efferent-Collectors 

 HYPOBEANOHIAL ARTERIES 



From the ventral angles of the second to the fifth (or sixth) efferent-collector 

 loops in Heptanchus, large commissural arteries (cm.-'°, figs. 151 and 153) 

 pass inward toward the middle line. Near their origin they are usually con- 

 nected by small vessels which, joined together, may be called the lateral hypo- 



