334 



FISHES 



hemibranchs of each branchial arch is conveyed to the dorsal 

 aorta by a single efferent vessel which corresponds to the more 

 anterior of the two in Mustelus antarcticus} 



(2) In CallorTiynckuB 2 among the Holocephali, where the 

 spiracle is absent but the hyoidean hemibranchi is still a true 

 gill, the latter organ is supplied with venous blood by a branch 

 from the ventral aorta, the corresponding efferent vessel joining 

 the dorsal aorta (Fig. 196). In the absence of a spiracular 



v\ a o nrir\nYannn 



my. a. 



the anterior 



carotid may be 

 regarded as con- 

 tinuous with the 

 hyoidean artery, 3 

 and as having its 

 origin directly 

 from the efferent 

 artery of the 

 hyoidean hemi- 

 branch (Fig. 

 196). At its 



FIG. 196. Portion of the efferent branchial system of Callo- origin the an- 

 rhynchus. a.c, Anterior carotid ; a.cb.a, anterior cerebral 



arteries ; d.a, dorsal aorta ; ef.b.a, 1-4, efferent branchial terior Carotid 



arteries; ef.hy, efferent artery from the hyoidean hemi- anastOHlOSeSWith 

 branch ; hy.c, hyobranchial cleft ; md.a, mandibular artery ; 



my.a, myelonal artery ; p.c, posterior carotid ; p.cb.a, pos- the mandibular 

 terior cerebral artery. (From T. Jeffery Parker. ) 



ar iei y. 



The Sturgeon more closely resembles the Elasmobranchs. 

 The hyoidean gill is supplied by an afferent branchial artery 

 from the ventral aorta, and its efferent vessel joins the corre- 

 sponding trunk from the holobranch of the first branchial arch. 

 A hyoidean artery supplies the spiracular pseudobranch, the 

 efferent vessel of which contributes to the blood-supply of the 

 brain and the eye, and probably represents an anterior carotid. 



Lepidosteus* offers a singularly interesting transition from the 



1 Note, however, that in the young Lepidosteus there are two efferent vessels 

 in each arch, which, nevertheless, differ from those of Mustelus in uniting to form 

 an epibranchial artery before joining the dorsal aorta (F. W. Miiller, Arch. Mikr. 

 Anat. xlix. 1897, p. 463). 



2 T. Jeffery Parker, op. cit. p. 691. 3 Cf. Figs. 195 and 196. 



4 Ramsay Wright, Journ. Anat. and Phys. xix. 1885, p. 482 ; F. "VV. Miiller, 

 op. cit. 



efrTj.ct. 



