. The biology of birds. Birds. ADAPTATIONS OF THE SKELETON 67 In the extinct Cretaceous Ichthyornis the vertebrae were amphicoelous (hollow at both ends, like a double egg-cup), which is the shape characteristic of fishes. It occurs, however, in many ex- tinct reptiles and in the extant geckos and the New Zealand "lizard," Sphenodon. It is rather interesting that the pro- coelous type of vertebra (hollow in front), which is commonest in modern reptiles, never occurs in birds. Several adaptations of the bird's backbone have been already noticed— the fusion of thoracic vertebrae in fly
. The biology of birds. Birds. ADAPTATIONS OF THE SKELETON 67 In the extinct Cretaceous Ichthyornis the vertebrae were amphicoelous (hollow at both ends, like a double egg-cup), which is the shape characteristic of fishes. It occurs, however, in many ex- tinct reptiles and in the extant geckos and the New Zealand "lizard," Sphenodon. It is rather interesting that the pro- coelous type of vertebra (hollow in front), which is commonest in modern reptiles, never occurs in birds. Several adaptations of the bird's backbone have been already noticed— the fusion of thoracic vertebrae in flying birds, to form a solid basis against which the wings can work ; the complex coalesced syn-sacrum to which the ilia are fused over a long stretch, to facilitate the balancing of the body in bipedal p^^ , progression ; and the terminal fusion of caudal vertebras in a plough- share which serves as a base for the tail feathers. It remains to notice that the neck is usually very long, with a very variable number (8-24) of very mobile vertebrae, whereas mammals, with four exceptions, have seven. The neck of the bird must be long enough to reach the ground and to reach the preen-gland. Dorsal vertebra of an ostrich. The upper one shows the anterior surface; the lower one the posterior surface. From a specimen. , neural spine; , transverse pro- cess ; A,z., anterior articular process ; , neural arch, in shelter of which the spinal cord lies ; c, the centrum or body; , posterior articular process ; R., facet for the head of a 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 Thomson, J. Arthur (John Arthur), 1861-1933. New York : Macmillan
Size: 1172px × 2133px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, booksubjectbirds, bookyear1923
