As in so many other details of its anatomy, _Neoceratodus_ exhibits in its arterial system abundant evidence of the wide-spreading affinities of the group to which it belongs. In its branchial arterial system _Neoceratodus_ presents a singular combination of features which, individually, are characteristic of Amphibia and Elasmobranchs. Special Amphibian features may be noted in the origin of the afferent branchial arteries almost simultaneously from the anterior end of the conus arteriosus; in the mode of union of the epibranchial arteries to form the dorsal aortae; in the origin of a lingual artery from the efferent vessel of the first branchial arch; and in the derivation on either side of a pulmonary artery from the fourth epibranchial artery. Agreement with Elasmobranchs is to be found in the presence of two efferent branchial vessels in each branchial arch, although the relations of these arteries are more primitive than in most adult Elasmobranchs, inasmuch as the two efferent vessels of the _same_ arch unite to form an epibranchial artery; and also in the origin and distribution of the anterior and posterior carotids. Lastly may be mentioned the fact that _Neoceratodus_ agrees not only with the Amphibia but also with those generalised Teleostomi, _Polypterus_ and _Amia_, in the mode of origin of the great arteries for the air-bladder. Of the two remaining Dipnoi, the arterial system of _Protopterus_[390] is better known than that of _Lepidosiren_, but in both cases further research is needed before a satisfactory comparison can be made with _Neoceratodus_ and other Vertebrates. It is evident, nevertheless, that both genera differ from _Neoceratodus_ in approximating more closely to the Amphibia than to the {340}lower Fishes, in so far as the branchial part of the arterial system is concerned. [Illustration: 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^2_, 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; _l.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.)]