yep) 
FISHES CHAP. 
which the first and last supply the anterior walls of the first pair 
of sacs and the posterior walls of the last pair respectively. Each 
of the remaining afferent vessels extends into an interbranchial 
Fic. 194.—Branchial arterial system 
of the Lamprey (Petromyzon flu- 
viatilis). The ventral aorta and 
the afferent branchial arteries are 
seen on the left side, and the effe- 
rent branchial and dorsal aorta on 
the right (diagrammatic). af.b.a, 
ef.b.a, Afferent and efferent bran- 
chial arteries ; a@.0, auditory organ ; 
6.c, branchial canal ; ¢.c, cephalic 
circle ; cm.a, coeliaco - mesenteric 
artery ; d.a, dorsal aorta ; e, eye ; 
ex.c, “external carotid” ; h, heart ; 
7.6.8, interbranchial septum ; 77.c¢, 
internal carotid ; oph.a, ophthal- 
mic artery ; 7.v.a, l.v.a, right and 
left ventral aorta; v.a@, median 
ventral aorta ; v.c, ‘‘ ventral caro- 
tid” ; 1-7, gill-sacs. (Modified 
from Vogt and Yung.) 
septum, and supplies the gill-lamellae 
of the posterior wall of one sac and 
those of the anterior wall of the 
next sac behind. The corresponding 
- efferent branchial vessels have a 
similar distribution, and unite dors- 
ally to form a median dorsal aorta. 
Beneath the base of the skull the 
latter vessel divides into two branches 
which, after receiving the first pair 
of efferent branchial vessels, pursue 
a divergent course forwards, but 
subsequently converge and unite to 
form a “circulus cephalicus,” as in 
Teleosts. From the cephalic circle 
are given off on each side (1) an 
“internal carotid” artery for the 
brain and eye; (2) an “external 
carotid” for the lateral and ventral 
walls of the head; and (3) a large 
ventral branch which supplies the 
lingual apparatus; while from the 
abdominal portion of the dorsal aorta 
are derived, first, a coeliaco-mesen- 
teric artery for the liver and ali- 
mentary canal, and subsequently 
branches for the myotomes, kidneys, 
and the gonad. The terminal por- 
tion of the aorta then enters the. tail 
and forms the caudal artery. 
In Elasmobranchs ! (e.g. Mustelus 
antarcticus) the undivided ventral 
aorta gives off five pairs of afferent 
branchial arteries which, on each side, ascend in succession the 
outer convex sides of the hyoid and first four branchial arches 
1 T. Jeffery Parker, Phil. Trans. 177, Pt. ii. 1886, p. 686; cf. H. Ayers, Bull. 
Mus. Comp. Zool. Harvard, xvii. No. 5, 1889, p. 191. 
