. Text book of zoology. Zoology. 4. Reptilia. 409 In the adult, tte skeleton is only to a slight extent carti- laginous ; it consists almost entirely of bone. The notochord has usually disappeared; only in the Geckos does it persist as a continuous cord extending the whole length of the vertebral column.* The centra usually articulate; they are generally proccelous; in the Crocodilia, there are cartilaginous discs between The vertebral column is usually divisible into more regions than in the Amphibia: first, there is a variable number of cervical vertebrse, without ribs or wit
. Text book of zoology. Zoology. 4. Reptilia. 409 In the adult, tte skeleton is only to a slight extent carti- laginous ; it consists almost entirely of bone. The notochord has usually disappeared; only in the Geckos does it persist as a continuous cord extending the whole length of the vertebral column.* The centra usually articulate; they are generally proccelous; in the Crocodilia, there are cartilaginous discs between The vertebral column is usually divisible into more regions than in the Amphibia: first, there is a variable number of cervical vertebrse, without ribs or with short ones; then a number provided with longer ribs, the thoracic vertebras; these are often followed by several ribless lumbar vertebrae; then the sacral vertebrse, usually two, to the transverse processes of which the pelvis is attached (occasionally, especially in certain extinct Reptilia, there is a larger numbers of sacrals); lastly, the caudal vertebrae,! without ribs. In the Snakes, however, in consequence â¢of the absence of limbs, these distinctions do not hold; all the cervical and dorsal vertebree, with the exception of the first, bear well-developed ribs; there are no sacrals, and therefore trunk and caudal vertebrae only can be distinguished. The first two cervicals, the atlas and axis, are peculiar in form (Fig. 333). The centrum "Fig. 333. Diagrammatic transverse section of the atlas of one of the higher Vertebrata. 6 ^ arch of the atlas, 1 odontoid process, m bony plate, I ligament.â â Orig. Fig. 334. Diagram of axis. 1 centrum of atlas, 2 centrum of axis, 62 ^^oTi of axis.âOrig. Fig. 333. ( I Fig. 334. k J. â¢of the former is fused with the second, forming a process (the odontoid) at its anterior end. The first vertebra is, therefore, merely a bony ring formed by an arch, bridged below by a bony * In the young Lacerta, etc., considerable portions of tlie chorda dorsalis are present in the centra, but they disappear later. fTransverse processes are
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