THE SKELETAL SYSTEM 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 postzyga- 

 pophysis 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 verte- 

 hrarterial 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 prezyga- 

 pophyses, but their articular surfaces are directed ven- 

 trally. Each pedicle is deeply notched posteriorly, form- 

 ing 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 tiihercle 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 sur- 

 face for the head of a rib. The tubercle of this rib articu- 

 lates with the posterior vertebra of the pair under con- 

 sideration. 



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 



