of certain Fishes of the Ganges. 35 



the osseous plate, which is connected with the anterior arch, 

 and afterwards proceeds upon its surface, where it divides and 

 subdivides into minute branches, distributed to the tip of the 

 supernumerary organ : the vessels that return the aerated 

 blood unite into one branch, which joins those proceeding 

 from the gills to form the aorta. 



Silurus Singio. Besides the eight branchial arches, there 

 are in this fish two respiratory canals, which extend along the 

 back from the cavity of the mouth to near the end of the tail, 

 where they terminate in blind extremities. They are situate 

 below the superior or dorsal portions of the lateral muscles, 

 one on each side of the vertebrae, close to their spinous pro- 

 cesses ; and are composed of two coats, of which the internal 

 one is smooth, vascular, and of a thin delicate texture, resem- 

 bling the membrane that covers the branchial laminae. Each 

 of these canals is provided with a large vessel, which injection 

 shows to be a continuation of that branch of the branchial ar- 

 tery sent to the posterior arch. It runs along the bottom of 

 the canal, giving off, as it proceeds to its posterior extremity, 

 numerous transverse branches that are minutely ramified upon 

 its internal surface. The canals open into the mouth ; but the 

 communication between them and that cavity, is in a great 

 measure shut up by the laminae of the second and third arches, 

 at. the junction of their limbs: these laminae are disposed in a 

 semicircular figure, and are so placed, in relation to each other, 

 as to present, when the two arches are approximated, a lami- 

 nated surface of an oval figure, to the mouth of each canal. 

 The air contained in these cavities is apparently separated 

 from the water, by means of the laminated body : and the 

 blood, thus oxygenated upon their internal surface, is convey- 

 ed by small vessels that descend between the transverse pro- 

 cesses of the vertebrae, to join the aorta.* 



All the species, possessing these supernumerary organs of 

 respiration, are very tenacious of life; surviving the infliction 

 of severe wounds, and living upon land for a much longer time 

 than other fishes. " In China, the species of the G. Ophiocc- 

 p/udux" according to Hamilton, " arc often carried alive in 



If a quill, open at both ends, be introduced through an incision, at the 

 Mile of the spine, into one of thete canals, bubbles of air will arise from it 

 simultini'ou.sly with thos disengaged from undo- the operculum. 



