180 



THE ELASMOBRANCH FISHES 



only to the sinus venosiis, the larger left one passes across the ventricle to unite 

 with the right (dorsal) coronary forming a strong continuous vessel. A branch 

 arising from this trunk on the ventricle passes across the conus to the left 

 ventral coronary'. 



It will be observed that at the ventral angles of the efferent-collector loops 

 are certain smaller nutrient vessels (n.a., fig. 166a) which supply arterial 



Fig. 170. The carotids and associated arteries. (From Hyrtl.) 



A. Acanthias. B. Zygaena. C. Haja. 



a.clJ., anterior dorsal artery; ce., coeliac axis; d.a., unpaired dorsal aorta; d.a}, paired 



dorsal aorta "vertebral artery"; hy.ef., hyoidean efferent; i.e., internal carotid; ml., mye- 



lonal artery to cord; or., orbital (stapedial) artery; ps., pseudobranchial artery; r.a., ramus 



anastomoticus; s.cl., subclavian; s.m., superior mesenteric. 



blood to the gills and surrounding tissue. In Dasyatis arteries are well devel- 

 oped both at the ventral and the dorsal angles of the loops. Here they are ac- 

 cessory efferent-collectors {ac, fig. 162) from accessory gills. 



AETEEIAL SUPPLY TO HEAD 



In the Elasmobranchs in general the two branches from the first efferent- 

 collector to the head are essentially like those noted in Heptanchiis. They often 

 differ, however, in extent of distribution. The first, the external carotid artery 

 (e.c, figs. 164 and 166a) , arises from the ventral angle of the hyoidean efferent- 

 collector and its branches are similarly distributed, as in Heptanchus. The 

 mandibular artery {m.a., fig. 167) extends toward the symphysis of the lower 

 jaw and supplies structures in this area. The hyoid artery runs upward be- 

 tween the hyoid and the mandibular arch, giving oft' twigs along its course. 



The second branch, the pseudobranchial, arising from the middle of the first 

 efferent-collector, differs greatly in the sharks and rays {ps., fig. 164) . Only in 



