Page:The Osteology of the Reptiles.pdf/108



spinal column or backbone of reptiles, as of all other air-breathing vertebrates, is made up of a variable number of separate segments called vertebrae. A vertebra (Fig. 73 ) is composed of a body, or centrum, and an arch, or neurapophysis, each ossifying separately and uniting at variable times, the neurocentral sutures more persistent than in most mammals, young or aquatic reptiles always (Fig. 87, ), adult land reptiles often showing them.



. 73. Anterior dorsal and cervical vertebrae: A, B, Sphenodon (Rhynchocephalia), anterior dorsal from the side and front; C, D, Iguana (Lacertilia), anterior dorsal from the side and front; E, F, Ophidia, anterior dorsal from behind and in front; G, Pteranodon (Pterosauria), cervical from the side, after Eaton.

Projections from the vertebrae, called processes or apophyses, serve for the attachment of muscles or ligaments, for articulation with adjacent vertebrae, or for the support of ribs, and are often characteristically different in different reptiles. Two pairs of processes springing from the arch, one in front and one behind, are