XII 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 
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; af.b.a, afferent branchial artery ; 
br.a, brachial artery ; ¢.m.a, coeliaco-mesenteric ; d.a, dorsal aorta; H, eye ; ep.a, 
epibranchial artery ; H, heart ; h.b.a, hypobranchial artery ; hy.a, afferent pseudo- 
branchial or hyoidean artery ; md.a, mandibular artery ; op.a, ophthalmic artery ; 
p.c.d, 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- 
