VASCULAR SYSTEM 



331 



(Fig. 195). The first or most anterior of these arteries supplies 

 the hyoidean hemibranch, while the succeeding four supply the 

 holobranchs of the four branchial arches. The blood is collected 

 from the capillaries of the branchial lamellae by a series of 

 efferent branchial vessels, a pair for the two hemibranchs of each 

 branchial arch and a single vessel for the hyoidean hemibranch, 

 which unite with one another in a somewhat singular fashion. 

 The efferent arteries from the anterior and posterior hemibranchs 

 of each branchial cleft unite above and below each cleft in such 



Gp.a>. 



p.ca. 



Fig. 195. — The branchial arterial system of Mustelus antarcticus. Left lateral view. 

 The ventral aorta and afferent branchial vessels are in solid black, the efferent 

 arteries and their branches have double contours. The branchial clefts have fringed 

 borders to indicate their hemibranchs, and the arches are in simple outline, a.c.a, 

 Anterior carotid; a.d.a, anterior dorsal aorta; a/.b.a, afferent branchial artery; 

 6r.a, brachial artery ; c.m.a, coeliaco-mesenteric ; d.a, dorsal aorta ; -E, eye ; ep.a, 

 epibranchial artery ; j?, heart ; h.b.a, hypobranchial artery ; hy.a, afferent pseudo- 

 branchial or hyoidean artery ; md.a, mandibular artery ; op.a, ophthalmic artery ; 

 p.c.a, posterior carotid ; sb.a, subclavian ; sp, spiracle ; v. a, ventral aorta ; 1-5, 

 the hyobranchial and four succeeding branchial clefts. The hypobranchial 

 artery is seen immediately beneath the ventral aorta. (After T. Jeffery Parker, 

 diagrammatic.) 



a way as to form a series of complete vascular loops round the 

 hyoidean cleft and the three succeeding branchial clefts, which 

 are connected by short longitudinal trunks in each arch and also 

 by a longitudinal commissural vessel between their ventral 

 extremities. As the fifth arch is gill-less, there is no complete 

 loop round the fifth cleft, the blood collected by the efferent 

 vessel of the posterior hemibranch of the fourth arch being 

 conveyed to the corresponding vessel of the anterior hemibranch 

 of the same arch by one of the short longitudinal vessels above 

 mentioned. Dorsally, each arterial loop is continuous with an 

 epibranchial artery ; and by the dorsal union of the four epi- 



