178 



THE ELASMOBRANCH FISHES 



BRANCHES OF EFFERENT-COLLECTOES 



HYPOBRANCHIAL ARTERIES 



The liypobraiichial arteries in Elasmobranchs form a most complex system of 

 vessels in the ventral walls and floor of the pharyngeal area. In general the 

 ventral ends of the different efferent-collector loops may be more or less com- 

 pletely connected by a longitudinal vessel which, f ollo^^^ng Parker and Davis, 

 I have termed in Heptanch us the lateral hypobranchial artery {l.lib., fig. 153) . 



This vessel sometimes forms a con- 

 tinuous ventral chain on each side 

 from the first to the fourth effer- 

 ent-collector loop (Mustelus, fig. 

 166) . In Rata erinacea, and some- 

 times in Carcharias littoralis, 

 according to Parker and Davis 

 (1899) , the lateral hypobranchial 

 may even include the fifth loop, 

 but there is considerable irregu- 

 larity about this. Whatever con- 

 nections the loops may make with 

 the lateral hypobranchials, how- 

 ever, the tendency is to make 

 them in the region of the second 

 and third liranchial arches rather 

 than from the first or last loops. 

 In other forms the lateral hypo- 

 branchial line is incomplete {Raja 

 clavata), and in still others a 

 lateral hypobranchial is absent 

 {Dasijatis clipterura, fig. 167). 

 Commissural arteries {cm.) may arise from the hypobranchial, at or pos- 

 terior to the angles of the efferent-collector loops, and pass toward the mid- 

 ventral line anterior to the third and fourth afferent arteries {Mustelns 

 antarcticus, fig. 166a) ; or only a single one may be present as is usual for 

 Squalus sucMii. The commissurals passing from the lateral hypobranchials 

 medially may meet paired median hypobranchials as in Heptanchus macula- 

 tus (fig. 153 and Hexanchus corinus, fig. 169) . Some evidence of paired median 

 vessels is also seen in Mustelns {m.lih., fig. 166) . In certain forms the commis- 

 sural may join an unpaired median hypobranchial as in Carcharias littoralis. 

 The commissures may be of a dorsal or a ventral type. In the former type 

 the artery passes to the median line above the ventral aorta, while in the latter 

 it passes below the ventral aorta. In Mustelns canis (fig. 166b) both com- 

 missures are of the ventral type; in S.cyllinm catnlns both are of the dorsal 



Fig. 167. Hypobranchial arteries, Dasyatis dip- 

 tenira. (Blanche Lillibridge, orig.) (For expla- 

 nation see fig. 166.) 



