. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. Fig. 27. Head of young Amphiuma showing the external gills, partially covered at the base by the backward extension of opercular fold. In the anura, on the other hand, the external gills are early- lost, and are replaced by internal gills upon the sides of the clefts, which, however, are said to be of ectodermal origin. Air-bladder. — From the pharyngeal or oesophageal region there arises also in most ganoids and teleosts the air- or swim-bladder. It starts as a diverticulum from the dorsal ^ wall of the phar- ynx, the dista
. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. Fig. 27. Head of young Amphiuma showing the external gills, partially covered at the base by the backward extension of opercular fold. In the anura, on the other hand, the external gills are early- lost, and are replaced by internal gills upon the sides of the clefts, which, however, are said to be of ectodermal origin. Air-bladder. — From the pharyngeal or oesophageal region there arises also in most ganoids and teleosts the air- or swim-bladder. It starts as a diverticulum from the dorsal ^ wall of the phar- ynx, the distal portion of which enlarges into a thin walled sac, the air-bladder or pneumatocyst; the proximal portion forms the pneumatic duct. This duct remains open throughout life in the ganoids and the lower tele- osts, but in the higher tele- osts it closes and is reduced to a fibrous cord.^ The bladder itself usually lies dorsal to the aorta and urogenital system next the vertebral column. In ^ Cope, however, claims that in Siren the embryonic gills are lost, and that the per- sistent gills of the adult are new structures. 2 The pneumatic duct empties laterally in some characinidae, ventrally in Polypierus^ into the oesophagus; but until the development is known, we cannot say how far this- condition is secondary. 3 The teleostei were formerly subdivided into physostomi, with permanent pneumatic duct, and physoclisti with it Fig. 28. Relations of the air-bladder to the alimentary canal, after Dean. Ay in most physostomous teleosts; B, in Ery- thrimis; C, in Folypterus, CalamoichthySy and Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Kingsley, J. S. (John Sterling), 1854-1929. New York, H. Holt and Company
Size: 1667px × 1498px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyorkhholtandcom
