VASCULAR SYSTEM 



335 



Elasmobranch to the Teleost. As indicated in the preceding 

 chapter, this Fish possesses both a hyoidean gill and a spiracular 

 pseudobranch (Figs. 197 and 198). The hyoidean gill is sup- 

 plied by an afferent artery direct from the ventral aorta, but the 

 proper efferent vessel of the gill, which primitively joined the 

 dorsal aorta, is suppressed, and the blood is collected into a 

 vessel, which, like the hyoidean artery in Elasmobranchs, becomes 

 the afferent artery of the spiracular pseudobranch. The latter 



ef.ct. 



*Os, hy.ps. 

 : - : -~ : ~^ ?.#.' 



FIG. 197. Blood-vessels of the spiracular pseudobranch and the hyoidean gill in Lepi- 

 dosteus. of. a, ef.a, Afferent and efferent vessels of the hyoidean gill ; af.ps.a, 

 ef.ps.a, afferent and efferent vessels of the spiracular pseudobranch ; ca, carotid 

 (posterior) ; d.a, dorsal aorta ; ef.b.a l ~ 4 , efferent branchial vessels ; hy.a, hyoidean 

 artery ; hy.h, hyoidean gill ; hy.ps, spiracular pseudobranch ; v.a, ventral aorta. 

 (From F. W. Muller, after Johannes Miiller.) 



artery unites, however, with 9, second hyoidean artery derived 

 from the efferent branchial vessel of the first branchial arch, and 

 represents the artery termed " hyoidean " in Teleosts. The 

 efferent vessel from the spiracular pseudobranch joins an internal 

 branch from the carotid artery, and then distributes its blood 

 both to the eye and the brain. 



In Teleosts, as already mentioned in a preceding chapter, 

 it is probable that the hyoidean hemibranch is suppressed, the 

 so-called hyoidean pseudobranch being a spiracular pseudo- 

 branch. The latter is now supplied by a " hyoidean " artery, 

 which has its oristin from the ventral end of the efferent 



