. Chordate morphology. Morphology (Animals); Chordata. between the cervicals and the 2 sacrals bear ribs. Since the thoracic and lumbar series are not distinct, these vertebrae collectively are called dorsals. About 6 dorsals have ribs con- nected with the sternum. Behind these complete ribs, the ribs shorten in a graduated series until the last presacral (the 24th or 25th vertebra), which has only a nubbin, is reached. The complete ribs, and those behind them, are distinctly single-headed, and lack an uncinate process. All of the dorsal (thoraco-lumbar) vertebrae have wide neural spines, and
. Chordate morphology. Morphology (Animals); Chordata. between the cervicals and the 2 sacrals bear ribs. Since the thoracic and lumbar series are not distinct, these vertebrae collectively are called dorsals. About 6 dorsals have ribs con- nected with the sternum. Behind these complete ribs, the ribs shorten in a graduated series until the last presacral (the 24th or 25th vertebra), which has only a nubbin, is reached. The complete ribs, and those behind them, are distinctly single-headed, and lack an uncinate process. All of the dorsal (thoraco-lumbar) vertebrae have wide neural spines, and distinct pre- and postzygapophyses. There are 2 sacrals supporting the pelvis, and nearly 50 caudals. From the fourth caudal to nearly the tip of the tail, each vertebra has a Y-shaped hemal or intercentral arch (caudal chevron). This arch articulates with the interverte- bral gap. The caudal vertebrae have tall neural spines tapering down and disappearing at about two-thirds of the length of the tail. Neural arches with pre- and postzyga- pophyses continue back nearly to the tip of the tail. The anterior caudal vertebrae have long transverse processes that double about one-third of the way back along the tail and take part in the formation of a vertical breakage line. in the middle of the body. About half way along the length of the tail, the transverse processes disappear, but the breakage lines occur to the tip of the tail. The vertebrae, with the exception of the atlas and axis, are procoelous— hollowed in front, but with a bulging articular surface be- hind (Figure 6-10). Tuatara The neural arches of Sphenodon do not retain the line of suture with the body as in the alligator, and an in- tercentrum is present between all of the vertebrae. There are 8 cervicals, unless one excludes the last, which bears a large nb. This rib, however, is without a costal segment attaching to the sternum. There is a small preatlas neural arch to either side in the ligament joining the atlas
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