334 FISHES CHAP. 
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 Callorhynchus* 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 
pseudobranch 
the anterior 
carotid may be 
regarded as con- 
tinuous with the 
hyoidean artery,* 
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 < F 
arteries ; d.a, dorsal aorta; ef.b.a, 1-4, efferent branchial terior carotid 
eters oy ferent, aia hom the Myce tem. anastomosesith 
my.a, wmyelonal artery ; p.c, posterior carotid; p.cb.a, pos- the mandibular 
terior cerebral artery. (From T. Jeffery Parker. ) artery. 
The Sturgeon more closely resembles the Elasmobranchs. 
The hyoidean gill is suppled 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 
? Note, however, that in the young Lepidostews there are two efferent vessels 
in each arch, which, nevertheless, differ from those of MJustelws 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. W. Miiller, 
op. Cit. 
