282 



RESPIRATION. 



vessels and epithelium This organ, however, 

 is further composed of a number of pecu- 



Fig. 230. 



Plan of blood-vessels in the gland (aerogenic?^) of the 

 air-bladder of the Cod-fish, showing the simply 

 looped character of the vessels. ( Original.) 

 a, a, indicate a stratum of fibres, vessels, and 

 epithelium lining the internal surface of the gland 

 in common with the whole interior of the air- 

 bladder. 



liarly arranged, elongated corpuscles, which 

 descend in two rows from each vascular 

 branch, and are bound together by a loose 

 cellular tissue : the corpuscles are beset 

 with fine villiform processes* Thus it should 

 be noticed that the veins as well as the 

 arteries concur to form the vaso-ganglions. 

 The vaso-ganglions of the eel and conger 

 are placed at the sides of the opening of the 

 air-duct, are "bipolar," and consist of arteries 

 and veins ; their efferent trunks do not ramify 



Fig. 231. 



Plan of the blood-vessels in the glands of the air- 

 bladder of the Eel. They consist of straight pa- 

 rallel ultimate vessels of uniform diameters, of 

 arteries, and veins, carrying streams of blood moving 

 in opposite directions. (OriginaL) 



in the immediate margin of the vaso-ganglion 

 from which they issue, as in the vaso-gan- 

 glion of the cod, turbot, acerine, and perch, 

 but run for some distance before they again 

 ramify to form the common capillary system 

 of the lining membrane of the air-bladder. 

 In the parasitic and suctorial dermopteri and 

 pleuronectida3 and ray-tribe the air-bladder 

 does not exist. 



The ductus pneumaticus exists in the eel, 

 sturgeon, amia, erythrinus, lepidosteus, lepido- 

 siren, polypterus. It is remarkable that in 

 these fishes the vaso-ganglion is not deve- 

 loped. " Under all diversities of structure 

 and function the homology of the swim- 

 bladder with the lungs is clearly traceable ; 

 and finally, in those orders of fishes which 

 lead more directly to the reptilia as, for 

 example, the salamandroid ganoidei and pro- 



topteri those further modifications are super- 

 induced by which it becomes also analogous 

 in function to the lungs of the air-breathing 

 amphibia." * 



The Lungs in the Batrachia. In the ichthioid 

 amphibia there exist two long membranous pul- 

 monary sacs, extending, like the air-bladder of 

 fishes, far backwards into the cavity of the 

 abdomen, above the other viscera, but freely 

 moveable in the cavity of the peritoneum, and 

 invested with this serous membrane. They 

 consist of smooth plane-walled sacs, and 

 communicate with the pharynx by means of 

 their membranous ducti pneumatici or tra- 

 cheas. This simple condition of the lungs 

 occurs in a permanent form in the salaman- 

 dridae. Each sac is provided with a pulmo- 

 nary artery, which runs in a straight course 

 along the outer side of the organ. From 

 this vessel, branches proceed with great regu- 

 larity at right angles and at definite distances. 

 From the midpoint of the space between the 

 arterioles, a venule arises to run round the 

 opposite semi-cylinder of the organ into the 

 chief trunk of the pulmonary vein. In con- 

 sequence of this regularity in the distribution 

 of the arteries and veins, the true capillary 

 interspaces present a regularity of area, ft 

 follows from this arrangement that each drop 

 of blood, in its passage from the extreme 

 artery to the extreme vein, undergoes in 

 every part of the lung the same quantum of 

 aeration. It is commonly supposed, by com- 

 parative anatomists, that the simple lungs of 

 the salamandridcB present a perfectly smooth 

 and uniformly plane surface internally, such 

 that every spot participates with equal acti- 

 vity in the office of aerating the blood. This, 

 however, is not the case. The septa which, 

 in the case of the frogs and toads, divide the 

 internal superficies into cells, exist in a rudi- 

 mentary state, but unquestionably in the lung 

 of the newt. They are indicated by inter" 

 seeling lines of vibratile cilia. They coincide 

 chiefly with the principal branches of blood- 

 vessels. Bundles of elastic fibres also run 

 parallel with the vascular trunks, which confer 

 upon these delicate organs an uncommon 

 amount of elasticity. To the next point in 

 the minute structure of the lungs especial 



* R. Owen, Cat. of Phys. Ser. of Coll. Sur. 4to, 

 1832-40; Mttller, J., Vergleichende Anatomic der 

 Myxinoiden : Abhand. Akad der Wissenschaften 

 zu Berlin, 1834 ; Agassiz, Hist, des Poissons Fos- 

 siles, 1833-45 ; Cuvier et Valenciennes, Histoire 

 Nat. des Poissons, 1845 ; De Blainville, Annales des 

 Sciences Naturelles, 1837 ; Bojanus, Versuch einer 

 Deutung der Knochen in Kopfe der Fische, in 

 Oken'slsis, 1818; Yarrell on British Fishes, 8vo, 

 1836; Paley, Nat. Theol. 8vo, ed. 10. 1805; Bre- 

 scher, Recherches sur 1'Organe de 1'Ouie des Pois 

 sons, 1838 ; Monro, The Structure and Physiology 

 of Fishes explained and compared with those of 

 Man and other Animals, fol. 1785; Scarpa, De Au- 

 ditu et Olfactu, 1789 ; Hunter, Obs. on the Ani- 

 mal Economy, Palmer's ed., 1837; Ratke, in 

 Die Physiologic von Burdach, 8vo, i. 1826 ; Allen 

 Thompson, Jameson's Journal, 1830-31 ; Duvernoy, 

 Sur le Me'canisme de la Respiration dans les Pois- 

 sons, in Ann. des Sc. Nat. 1839; De la Roche, Obs. 

 sur la Vessie Aerienne des Poissons, Ann. du Mu- 

 seum, t. xiv. 1809. f 



