340 



FISHES 



CHAP. 



lower Fishes, in so far as the branchial part of the arterial system 

 is concerned. 



In their origin from the conns the four afferent branchial 

 arteries of Protopterus resemble those of Neoceratodus, 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 



-1-p.a. 



l.a.. 



FIG. 201. Branchial arterial system of Protopterus (diagrammatic), a, Auricle ; a.c.a, 

 carotid artery ; af.b.a 1 ~ 4 , afferent branchial arteries ; af, ef, afferent and efferent 

 vessels of the hyoidean pseudobranch ; b.a?, second branchial arch, the vestigial 

 first arch being omitted ; c.a, conns arteriosus ; e.g, external or cutaneous gill ; 

 ep.a, epibranchial artery ; hy.ar, hyoid arch ; hy.ps, hyoideau pseudobranch ; I. a, 

 lingual artery ; l.d.a and r.d.a, right and left dorsal aortae ; l.p.a, left pulmonary 

 artery ; s.v, sinosus venosus ; v, 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. 1 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. 



