A treatise on zoology . is supplied to the bladder in Polypterus and in the Dipnoi bypaired afferent pulmonary arteries, derived from the last (fourth)branchial arch, the sixth of the embryonic series (Fig. 197). Theblood is returned to the heart in Polypterus by paired efferent vessels,opening into the hepatic vein near the sinus venosus ; in the Dipnoiby paired vessels uniting and passing directly to the sinus venosusitself on the left side. That the air-bladder of the Dipnoi wasoriginally ventral, and that its dorsal position has been secondarilyacquired, is clearly shown by the course of t
A treatise on zoology . is supplied to the bladder in Polypterus and in the Dipnoi bypaired afferent pulmonary arteries, derived from the last (fourth)branchial arch, the sixth of the embryonic series (Fig. 197). Theblood is returned to the heart in Polypterus by paired efferent vessels,opening into the hepatic vein near the sinus venosus ; in the Dipnoiby paired vessels uniting and passing directly to the sinus venosusitself on the left side. That the air-bladder of the Dipnoi wasoriginally ventral, and that its dorsal position has been secondarilyacquired, is clearly shown by the course of the ductus pneumaticus,and of the left afferent and the left efferent vessels which pass round OSTEICHTHYES below the oesophagus towards the right side (Parker [324], Spencer[413]). Moreover, in the embryo, the bladder develops as amedian ventral outgrowth (Semon [399], Neumayer [308&]). In all the Actinopterygii the air-bladder is essentially a mediandorsal organ, lying below the vertebral column and aorta and above. Fig. l;i7. Diagrams illustrating tlie blood-supply of the aii-bladder in A, rolypttnis, B, Ceratoilvs, C,Amia, and D, a Teleost. The blood-vessels are seen from behind, and cut short in transversesection, n, dorsal aorta; , anterior dorsal artery from the coeliac ; a.«.v, ant. ventralartery ; , air-bladder ; , anterior dorsal vein to the cardinal; 608, 4th aortic arch (6thof the series); cv, coeliac artery ; d, ductus Cuvieri ; la, left pulmonary artery ; oe, oesophagus ;pr, portiil vein receivint; posterior vein from air-blad<ler ; , right pulmonary artery; V, right (branch oQ pulmonary vein ; /•;?, right vein from air-bladder ; v, left pulmonaryvein. the alimentary canal, often outside the abdominal coelom. Thecommunicating ductus pneumaticus jmsses down the dorsalmesentery to open into the oesophagus. The ductus isshort, and the opening wide in the more primitive forms {Lepi-dosteus, Amia, Acipcnser). But although the bladder is dorsal
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