Page:Laboratory Manual of the Anatomy of the Rat (Hunt 1924).djvu/41

27 The centrum is dorsoventrally flattened. The spinous process is a low pointed crest. The prezygapophysis, borne by the pedicle, is ovoid when viewed from above. Its articular surface is directed dorsomediad. The postzygapophysis is directly behind it, is similar in shape, and its articular surface is ventrolaterad. The transverse process, attached at the base of the pedicle, is pierced in the region of attachment by the foramen transversarium. The vertebrarterial canal comprises the transverse formina of the cervical vertebrae. It terminates with the sixth cervical vertebra.

The centrum of the fifth thoracic vertebra is nearly cylindrical. The spinous process is long and tapering; its point is directed caudally. There is a notch on the anterior edge of the laminae. This notch is flanked on each side by the oval prezygapophyses whose articular surfaces face dorsally. The postzygapophyses lie behind the prezygapophyses, but their articular surfaces are directed ventrally. Each pedicle is deeply notched posteriorly, forming an intervertehral foramen, for the passage of a spinal nerve. The transverse process of each side is situated between the anterior and posterior zygapophyses. The articular surface of the transverse process, facing laterally, supports the tubercle of a rib. A depression, the costal demifacet, will be observed at each end of the centrum near its dorsal border. The adjacent demifacets of two successive vertebrae combine to form the articular surface for the head of a rib. The tubercle of this rib articulates with the posterior vertebra of the pair under consideration.

The fourth lumbar vertebra's centrum is cylindrical ventrally, but flattened above. The spinous process is a laterally compressed plate which runs the whole length of the vertebra, is somewhat triangular in shape, and leans