Page:Natural History Review (1861).djvu/330

318 branchial arch, whose epibranchial segment (Owen) is expanded into a broad triangular plate; the accessory organ lies upon this plate in such a manner, that the axis of its spiral canal keeps a perpendicular direction throughout.

The right and left organs communicate by a common aperture with the roof of the pharynx, immediately behind the toothed pharyngo-branchial segments (Owen, pharyngiens superieurs Cuv.) The lining membrane of these organs is very vascular, and fine injection proved beyond contradiction, that their arteries are but prolongations of those which bring the venous blood to the gills. Their veins unite with the root of the aorta, and must, therefore, contain arterialised blood. On the inner border of the twisted tube there is a double row of fringes, of the consistency of cartilage, and a groove lies between the two rows, but there is no interspace like a branchial cleft.

Our great anatomist Johannes Müller, threw out a hint of the existence of this organ in his admirable work "Bau und Grenzen der Ganoiden," p. 74 et seq.; but the specimen which he had for dissection was probably so defective as to cause him entirely to overlook its peculiar snail-like convolution, and he only speaks of the above mentioned double series of fringes, which he declared to be a true biserial gill. Careful investigation of well injected preparations, has, however, satisfactorily convinced me, that the biserial gill of Müller is not a respiratory gill, but simply a continuation of the peculiar horny fringes, which are attached to the concave border of the branchial arches in many Clupeid and Scomberoid fish, and which serve as combs, or gratings, to intercept any solid particle swallowed, which if forced through the interspaces of the branchial arches would, most certainly, injure the very delicate vascular net-work, supported by the slender and compressed processes of the gill fringes.

A very large branch of the pneumogastric nerve supplies the inner side of this organ (to which I give the name of Cochlea branchialis), and it strikes me that its mucous membrane may be capable of receiving some special sensation. The organ is surrounded by a strongly developed muscular coat, so that the water contained in it can, by the contraction of the muscles, be easily expelled through the same orifice by which, on dilatation, it enters.

On a former occasion I have pointed out that some of the true clupeid fish, as Meletta, Chatoessus, Chipanodon, Gonostoma, &c