340 FISHES CHAP. 
lower Fishes, in so far as the branchial part of the arterial system 
is concerned. 
In their origin from the conus the four afferent branchial 
arteries of Protopterus resemble those of eoceratodus, but their 
relations to the branchial clefts are somewhat different (Fig. 
201). The first or hyoidean cleft is closed, and the first afferent 
vessel lies between the second cleft and the third, and is there- 
fore in relation with the second branchial arch. The remaining 
afferent arteries are disposed between the succeeding clefts and 
Fic. 201.—Branchial arterial system of Protopterus (diagrammatic). a, Auricle; a.c.a, 
carotid artery ; af.b.a1-4, afferent branchial arteries; af, ef, afferent and efferent 
vessels of the hyoidean pseudobranch ; 6.a7, second branchial arch, the vestigial 
first arch being omitted; c.a, conus arteriosus ; e.g, external or cutaneous gill ; 
ep.a, epibranchial artery ; hy.ar, hyoid arch ; hy.ps, hyoidean pseudobranch ; /.a, 
lingual artery ; /.d.a and 7.d.a, right and left dorsal aortae ; d.p.a, left pulmonary 
artery ; s.v, sinosus venosus ; ¥, ventricle ; 2-6, the second branchial and succeeding 
clefts, the hyobranchial cleft being closed. The vestigial first branchial arch is not 
shown. The epibranchial arteries unite to form the right or left dorsal aorta at the 
same point and not in succession as in the figure. (Altered from Newton Parker.) 
are related to the corresponding arches. As the second and third 
arches, like the vestigial first arch, bear no gill-lamellae, their 
afferent arteries are directly continuous with the corresponding 
efferent vessels, as in those Teleosts in which certain arches are gill- 
less, as well as in the Tadpole-stage of the tailless Amphibia when 
the internal gills begin to degenerate ; and they apparently transmit 
arterial blood directly to the dorsal aorta.’ The third and fourth 
afferent arteries, on the contrary, supply venous blood to the two 
hemibranchs which are borne by each of the two corresponding 
arches, viz.: the fourth and fifth, and from each pair of hemibranchs 
the blood is collected into two efferent vessels which unite dorsally 
1 According to Boas ; for reference, see p. 329. 
