. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. 54S Biology of the Vertebrates South America, which finds an elongated thoracic basket useful since it spends most of its time suspended upside down from the limbs of trees. True ribs, that reach the sternum directly by means of their own cartilage segments, vary from two pairs in the sea-cow Trichechus, to ten pairs in the agile spider monkey Ateles. 2 ^^.-â 'Metacarpals c<^âPhalanx. Coracoid r\ ⢠i \0^3i§-C- Scapula ClavicleN />WiâviTii T^bs^ â â
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. 54S Biology of the Vertebrates South America, which finds an elongated thoracic basket useful since it spends most of its time suspended upside down from the limbs of trees. True ribs, that reach the sternum directly by means of their own cartilage segments, vary from two pairs in the sea-cow Trichechus, to ten pairs in the agile spider monkey Ateles. 2 ^^.-â 'Metacarpals c<^âPhalanx. Coracoid r\ ⢠i \0^3i§-C- Scapula ClavicleN />WiâviTii T^bs^ â â ⢠1/ \\7 L IJluQm\â "'urn \v v^^Jn/i^f^Wt/^L Uncinate Process \:\ ^////iJr^rFemur Keel^\V%=^>/! \\^\ Sternum^^^f Y\ylschium Sternal Part'^ok^ "\ \\ Vertebral Part Ribs ^~P"bis Fig. 459. A part of the skeleton of a goose, showing uncinate processes. (After Kingsley.) 3. The Sternum, or Breastbone As contrasted with the backbone the frontbone, or sternum, is the ter- restrial part of the thoracic basket, that is it appears first in the evolutionary history of vertebrates that locomote on land. The need of such a strengthening structure to knit together the whole thoracic basket into a firm skeletal unit on which the muscles of the anterior legs or arms may find suitable anchorage, is not apparent for the more primitive water-dwellers like fishes that go forward by lateral tail motion rather than by the leverage of bilateral appendages. Not only fishes are devoid of any kind of sternal apparatus, but also some of the lowest urodeles, for instance, Proteus and Amphiuma, as well as the footless caecilians, snakes, and turtles. The sternum develops in the ventral median septum of the anterior trunk or thoracic region of tetrapods. In amniotes it forms the ventral ele- ment which, with ribs and vertebrae, completes the thorax. The earliest structure recognized as a sternum is found in urodeles. In Necturus (Fig. 460) it is a rather insignificant appeari
Size: 2232px × 1120px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, booksubjectanatomycomparative, booksubjectverte
