. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. The Skeleton 545 an inch long to approximately a foot in length, may nearly encircle the body. In fetal life ribs are not only present upon the seventh cervical vertebra but also upon all the lumbar vertebrae (Fig. 455). Moreover, rudiments of ribs, which afterwards fuse with the centra to form the lateral masses of the sacrum, are attached to the sacral vertebrae (Fig. 443). Ribless vertebrates include amphioxus, the cyclostomes, holocephalans, skates, an
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. The Skeleton 545 an inch long to approximately a foot in length, may nearly encircle the body. In fetal life ribs are not only present upon the seventh cervical vertebra but also upon all the lumbar vertebrae (Fig. 455). Moreover, rudiments of ribs, which afterwards fuse with the centra to form the lateral masses of the sacrum, are attached to the sacral vertebrae (Fig. 443). Ribless vertebrates include amphioxus, the cyclostomes, holocephalans, skates, and such lophobranchs as Syngnathus and Hip- pocampus among the teleost fishes. In the ganoid Polyodon, the ribs are quite vestigial. Among other fishes there are two sorts of ribs of diverse origin, namely, ventral and dorsal ribs, both of which are connected at one end with the vertebral column, although entirely unattached at the other end in the absence of a sternum (Fig. 456). Ventral ribs simply represent vertebral haemal arches, anterior to the anus, that have spread apart enough to incompletely encircle the body cavity (Fig. 456c. They are therefore sometimes known as haemal ribs. They lie entirely inside the muscles of the body wall, next to the peritoneal lining of the body cavity at the points where the myocommata join this layer. The ribs of the dipnoi, as well as of most teleosts and ganoids, are of this character. Dorsal ribs, on the other hand, grow out from the transverse processes of the vertebrae at the points where the myocommata cross the horizontal septum. They therefore extend between the dorsal and ventral groups of muscles that form the body wall (Fig. 456a) . Most elasmobranchs, together with all vertebrates above fishes, have dorsal ribs. In elasmobranchs and modern amphibians these are short and insignificant; but, beginning with reptiles, they become longer, in many instances encircling the body cavity and joining at the ventral ends with the breastbon
Size: 1120px × 2230px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, booksubjectanatomycomparative, booksubjectverte
