3 5^ SMITHSONIAN MISCELLANEOUS COLLECTIONS [vOL. 45 



tenth, eleventh, and twelfth thoracic vertebrse, as a rule, the trans- 

 verse process is absent, the ribs attached to these vertebrae articulat- 

 ing with the facets on the sides of the bodies only. In each of the 

 last four thoracic vertebrae, each transverse process is replaced by 

 a metapophysis on the anterior part of the vertebra, usually indicated 

 by a tubercle on the eighth thoracic, and steadily increasing in size 

 through the twelfth thoracic and still further increasing in size on 

 the lumbar vertebrae. On the side of each of the four above vertebrae 

 posteriorly, there is found another process, smaller than the above, 

 the anapophysis. It is first seen in the ninth thoracic, is usually 

 largest on the tenth, and decreases in size on the eleventh and twelfth. 

 The large transverse processes which are found on the lumbar series 

 are represented on the eleventh and twelfth thoracic by low lateral 

 ridges. 



The spinous or neural process of the first thoracic vertebra is very 

 short and broad, inclined slightly backw^ard. The neural spines of 

 the succeeding eight vertebrae are all broad at the base, but spine- 

 like at the free extremity, all are strongly directed backward. The 

 spine of the ninth thoracic is broader than the spines of the vertebrae 

 in front of it. The spine of the tenth thoracic vertebra is still 

 broader from before backward, and usually the spine of this vertebra 

 is inchned neither forward nor backward, that is, as the rule, it is 

 the anticlinal vertebra. The spines of the eleventh and twelfth 

 are still broader, and like the spinous processes of the lumbar verte- 

 bras are directed forward. 



The first vertebra presents a whole facet at the anterior edge of 

 the centrum for the head of the first rib, a half facet at the posterior 

 edge of the centrum for half of the head of the second rib. From 

 the second to the eighth thoracic vertebrae, inclusive, there is a half 

 facet at the anterior edge and another half facet at the posterior 

 edge of the centrum. The ninth thoracic vertebra has only a half 

 facet at the anterior edge of the centrum. The tenth, eleventh, and 

 twelfth have a whole facet each on the centrum anteriorly. 



The transverse process of the first thoracic vertebra has a small 

 concave facet for articulating w'ith the tubercle of the rib. All the 

 other vertebrae to and including the ninth have similar facets which 

 increase in size up to the fifth and then decrease in size again. The 

 tenth, eleventh, and twelfth thoracic vertebrae have no transverse 

 processes. 



Variations in the thoracic vertebrae are fewer than they are in the 

 cervical vertebrae of the Leporidae. Some of the variations do not 



