338 



FISHES 



of the corresponding veins, the two genera exhibit a significant 

 resemblance to the Dipnoi. 



In the Dipnoi the ventral aorta is so short that the afferent 

 branchial arteries arise almost directly from the conus arteriosus 

 with their roots in close contiguity to one another (Fig. 200). 



In Neoceratodus (Fig. 200), 1 there are two efferent vessels to 

 each gill-bearing branchial arch, which unite above to form an 

 epibranchial artery, and by the successive union of the four 



(t.cb.a.. 



-p.cb.cts. 



OC.Ct. 



FIG. 200. Branchial arterial system of Neoceratodus. Lateral view. The conus arteriosns 

 and the afferent branchial vessels are represented in solid black, the efferent vessels 

 and their derivatives with double contours, a, Auricle ; a.c.a, anterior carotid ; 

 a.cb.a, anterior cerebral artery ; af.b.a', first afferent branchial artery ; br.a, 

 brachial artery ; c.a, coronary artery ; c.ar, conus arteriosus ; c.m.a, coeliaco- 

 mesenteric ; ep.a, epibranchial artery ; hb.a, hypobranchial artery ; hy.a, hyoid 

 artery ; hy.ar, hyoidean arch ; 1. a, lingual ; l.d.a, r.d.a, left and right dorsal aortae ; 

 oc.a, occipital artery ; oes.a, oesophageal artery ; p, pericardium ; p.a, pulmonary 

 artery ; p.c.a, posterior carotid ; p.cb.a, posterior cerebral artery ; s.v, sinus 

 venosus ; v, ventricle ; 1, hyobranchial cleft ; 2-5, branchial clefts. (After Baldwin 

 Spencer, diagrammatic.) 



epibranchial arteries a short common trunk is formed on each 

 side. Posteriorly, the two trunks unite to form a median 

 dorsal aorta. Immediately above the gill-clefts each efferent 

 vessel gives off a branch which, passing either forwards or back- 

 wards, unites with the corresponding branch of the efferent vessel 

 in front or behind as the case may be. A hyoidean artery 

 arises from the ventral extremity of the anterior efferent artery 

 of the first branchial arch, and, after giving off a lingual artery, 

 ascends the hyoid arch and supplies the hyoidean pseudobranch. 

 The efferent vessel of the pseudobranch (a.c.a) or anterior 

 1 Baldwin Spencer, Macleay Memorial Volume, 1892, p. 1. 



