330 



TISHES 



inc. 

 o.c.- 

 a.o.- 



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 

 of the Lamprey (Petmmyzon flu- ven tral branch which supplies the 



viatilis). The ventral aorta and ^ 



the afferent branchial arteries are lingual apparatus ; while irom the 



seen on the left side, and the effe- abdominal portion of the dorsal aorta 



rent branchial and dorsal aorta on r 



the right (diagrammatic), af.b.a, are derived, first, a coeliaco-mesen- 



efb.a, Afferent and efferent bran- t { . f th liyer d u _ 



chial arteries ; a.o, auditory organ ; * 



b.c, branchial canal ; c.c, cephalic mentary canal, and subsequently 



branches for the myotomes, kidneys, 



cm.a--- 



FIQ. 194. Branchial arterial system 



circle; cm.a, coeliaco - mesenteric 

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



ex. c," external caro tid "; h, heart; and the gonad. The terminal por- 



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



tion oi the aorta then enters the tail 



internal carotid 



in. c, 



oph.a, ophthal- 

 mic artery ; r.v.a, i.v.a, right and a nd forms the caudal artery. 



left ventral aorta ; v.a, median . . , _, , 



ventral aorta ; v.c, "ventral caro- In Elasmobranchs x (e.g. Mustel-US 



tid"; 1-7, gin-sacs. (Modified antarcticus) the undivided ventral 



from Vogt and Yung.) . 



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. 



