THORAX. 



BONES. 



Thoracic or Dorsal Vertebrae. There are twelve, distin- 

 guished by having facets for the ribs. The body is heart- 

 shaped, slightly thicker behind than in front, and of nearly 

 equal length and breadth ; from the second to the ninth inclu- 

 sive each has four costal demi-facets, an upper pair on the upper 

 margin near the junction of the pedicle, and a lower pair on 

 the lower margin just in front of the invertebral groove. The 

 pedicles are short, thick, and directed backward and slightly 

 upward; the superior notch is shallow and the inferior deep. 

 The lamina; are broad and flat with sharp margins; the upper 

 overlap the lower. The spinal foramen is small and nearly 

 circular. The spines incline downward, overlap, and end in 

 tubercles; they are triangular at the base but compressed 

 laterally elsewhere ; the middle ones are the longest and most 

 oblique. The transverse processes run backward, outward, and 

 slightly upward ; they end in an enlargement on whose front 

 is a circular facet for the tubercle of the rib; they decrease in 

 size from above downward. The superior articular processes 

 are vertical with their facets directed backward and slightly 

 upward and outward; the inferior have their facets directed 

 forward and slightly downward and inward. [80] 



Peculiar Vertebrae. The first has a whole facet on the side 

 of its body, for the first rib; and a demi-facet on its lower edge, 

 for the second rib ; the superior articular surfaces look back- 

 ward and upward ; the body and spine resemble those of the 

 seventh cervical. The ninth may have only the upper demi- 

 facets. The tenth may have either a single whole facet on its 



[107] 



