Characteristics of the Vertebrata. Ixxiii 



as also in certain Muraenoid Teleostei, more or fewer of the 

 branchial arches fail to develope gills^ and the direct connections 

 between the sub-branchially placed bulb and the sub-verteljrally 

 placed aorta^ which in other Fishes exist only in the foetal state, 

 persist here throughout life. From each of the posterior aortic 

 arches {Lejndoslren paradoxa), or from each of the compound factors 

 of the dorsal aorta made up on each side {Bhlnocrijptis annedens), a 

 branch is given off to the cellular air sac ; and during the period in 

 which these animals live out of the water, the aeration of their 

 blood is dependent upon the ramifications thus formed there. The 

 vein which brings the blood from the pulmonary air sacs back to 

 the heart, instead of opening into the portal or hepatic vein, as the 

 veins from the air-bladders of ordinary Fishes do, or into a vena 

 cava inferior, as does the vein from the air-bladder of the Ganoid 

 Poli/jjterus bichir, opens independently into the ventricular cavity 

 after dilating within the pericardium ; and thus, though diverg'ing 

 but a very little from the arrangements common in (uni-aurieulate) 

 Fishes, it constitutes a system analogous to and homologous with the 

 pulmonary veins and auricles of higher Vertebrata. Ordinarily in 

 Fish, the blood from the parts of the body posterior to the heart 

 exclusively of the chylopoietic viscera, is collected into the tvro 

 sul)vertebral venae cardinales, which meet the two venae jugulares 

 from the anterior parts of the body, and form with them the trans- 

 verse ductus Cuvieri which open into the sinus venosus. The hepatic 

 veins, which bring the blood of the chylopoietic viscera back to the 

 heart, very ordinarily end by opening* into the sinus venosus, with- 

 out receiving any factors from any other than those organs. A true 

 vena cava inferior is constituted in some Fishes, as in the Perch 

 amongst Teleostei, and in the Poltjpterus amongst Ganoidel, by the 

 fusion either of veins from the air-bladder with veins from the 

 genital glands as in the former of the two Fishes named, or of a 

 vena cava sub-vertebralis irapar with veins from the bifid air-bladder 

 as in the latter. A renal-portal system is present, except in the 

 Marslp>ohrancMi ; it is constituted either by caudal and dorsal veins 

 both or by the latter only ; and anastomoses, though not always, 

 with the hepatic portal system. 



The Teleostei, Ganoidei, Dipnoi, and Chiniaerae have free oper- 

 cular valves covering a, more or less extensive branchial cavity. 

 The gills of Teleostei are ordinarily four, and are never more than 



