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92 for the peculiar saddle-shaped articulations of the cervical vertebrae of birds.

On the dorsal side of the arch, in the middle, is the spine or neurapophysis, of extremely variable size and length, sometimes rudimentary, sometimes very long. As a rule, the spines are longest and stoutest at the beginning of the dorsal series, for the attachment of muscles and ligaments controlling the neck and head. The spines are always short in legless or slender crawling reptiles (Fig. 73 ) and are never long or slender in aquatic reptiles, in front at least. The spines of most sauropod dinosaurs in front of the sacrum are broadly divided, V-shaped, doubtless for the lodgment of stout muscles and ligaments used in controlling the long neck.

A longer or shorter process on the sides of the arch for the support in part or wholly of the ribs is known as a diapophysis (Fig. 73, 75). A like process or facet on the side of the centrum anteriorly for articulation of the head of the rib is called a parapophysis (Fig. 73 ). Either is commonly called a transverse process, and the same term is often applied to a like process on the sides of the caudal vertebrae, of which probably the anterior ones, at least, in all cases are merely coössified ribs.

A process, paired or single, on the under side of the vertebrae, is properly called a hypapophysis (Figs. 73, 75 ). Hypapophyses are characteristic of snakes, often as far back as the tail; in some instances they are developed to serve as a sort of masticatory apparatus for the crushing of eggs in the stomach. They also often occur on the cervical vertebrae of lizards, crocodiles, and turtles. Paired hypapophyses (lymphapophyses) are characteristic of the caudal vertebrae of snakes, where they replace the absent chevrons.

When the ends of the centra are concave, as they are in all early reptiles, nearly all fishes, and most amphibians, the vertebrae are known as amphicoelous (Fig. 74). If the cavities are deeply concave, communicating with each other through the centrum, the vertebrae are called notochordal; that is, the notochord was continuous in life. And this was the primitive condition found in the Cotylosauria (Fig.