Elements of comparative anatomy (1878) Elements of comparative anatomy elementsofcompar00gege Year: 1878 BRANCHLE OF VERTEBRATA. 543 pouch in front,, and the anterior wall of the one behind. While the pouches communicate with the pharyngeal cavity by narrow orifices, which are bounded by the cartilaginous branchial arches, they also open on the side (or in Rays, on the ventral surface) of the body by just as many clefts. Rows of branchial lamella; lie in the walls of the branchial pouchesâ in the embryonic condition these lamella* develop filamentous prolongations, which form the external gil
Elements of comparative anatomy (1878) Elements of comparative anatomy elementsofcompar00gege Year: 1878 BRANCHLE OF VERTEBRATA. 543 pouch in front,, and the anterior wall of the one behind. While the pouches communicate with the pharyngeal cavity by narrow orifices, which are bounded by the cartilaginous branchial arches, they also open on the side (or in Rays, on the ventral surface) of the body by just as many clefts. Rows of branchial lamella; lie in the walls of the branchial pouchesâ in the embryonic condition these lamella* develop filamentous prolongations, which form the external gills. These are also found on the spiracular cleft. The anterior wall only of the last branchial pouch is provided with a gill (Fig. 300, A). From this arrangement we may derive what we find in the Ganoidei, and from that what we find in the Teleostei. The spiracular gill, which has no respiratory function in the adult state of the Selachii, is the first to undergo the A greatest degenera- tions. In some Ganoidei, which possess a spiracle ( Acipenser), the gill is con- verted into a Pseudobranchia (a gill which has lost its proper branchial artery and vein); this is not found in Poly- pterus nor Amia. In the Osseous Fishes it also ap- pears to be wanting*, or has lost all re- semblance to a gill. The anterior series of branchial lamellas of the Selachii, that, namely, which is attached to the posterior face of the hyoid arch, is also found among the Ganoidei, where it forms a respiratory opercular gill (Acipenser, Lepidosteus). It is found also during the embryonic stages of the Teleostei, but it does not persist. It sometimes consists of a short row of lamellas, which is attached to the operculum; sometimes it is carried to the base of the skull, and sometimes it is hidden below the mucous membrane. Even when in this condition, rudi- mentary cartilaginous rods may be found in it. When still more degenerated, it forms a glandular structure, which is made up of several lobule
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