330 



FISHES 



iric. 

 o.c. 

 a.or 



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 



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 



cm. a. 



Fig. 194. — Branchial arterial systeni 

 of the Lamprey {Fetromyzon Jiu- 

 viatilis). Tlie 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.h.a, Afferent and efferent bran- 

 chial arteries ; a.o, auditory organ ; 

 b.c, branchial canal ; c.c, cephalic 

 circle; cm.a^ coeliaco - mesenteric 

 artery ; d.a, dorsal aorta ; e, eye ; 

 exx, " external carotid " ; 7i, heart ; 

 i.b.s, interbranchial septum ; in.c, 

 internal carotid ; oph.a, ophthal- 

 mic artery ; r.ti.a, l.v.a, right and 

 left ventral aorta ; v. a, median 

 ventral aorta ; vx^ " ventral caro- 

 tid " ; 1-7, gill-sacs. (Modified 

 from Vogt and Yung.) 



' T. Jeffery Parker, PUl. Trans. 177, Pt. ii. 1886, p. 

 Mus. Com,2]. Zool. Harvard, xvii. No. 5, 1889, p. 191. 



1 ; cf. H. Ayers, Bull. 



