104 



OSTEOLOGY 



The first, ninth, tenth, eleventh, and twelfth thoracic vertebrae present certaii 

 peculiarities, and must be specially considered (Fig. 91). 



The First Thoracic Vertebra has, on either side of the body, an entire articular 

 facet for the head of the first rib, and a demi-facet for the upper half of the head 

 of the second rib. The body is like that of a cervical vertebra, being broad trans- 

 versely; its upper surface is concave, and lipped on either side. The superior 

 articular surfaces are directed upward and backward; the spinous process is thick, 

 long, and almost horizontal. The transverse processes are long, and the upper 

 vertebral notches are deeper than those of the other thoracic vertebrae. 



The Ninth Thoracic Vertebra may have no demi-facets below. In some sub- 

 jects however, it has two demi-facets on either side; when this occurs the tenth 

 has only demi-facets at the upper part. 



The Tenth Thoracic Vertebra has (except in the cases just mentioned) an entire 

 articular facet on either side, which is placed partly on the lateral surface of the 

 pedicle. 



In the Eleventh Thoracic Vertebra the body approaches in its form and size 

 to that of the lumbar vertebrae. The articular facets for the heads of the ribs 

 are of large size, and placed chiefly on the pedicles, which are thicker and stronger 

 in this and the next vertebra than in any other part of the thoracic region. The 

 spinous process is short, and nearly horizontal in direction. The transverse processes 

 are very short, tuberculated at their extremities, and have no articular facets. 



The Twelfth Thoracic Vertebra has the same general characteristics as the- 

 eleventh, but may be distinguished from it by its inferior articular surfaces being 

 convex and directed lateralward, like those of the lumbar vertebrae; by the general 

 form of the body, laminae, and spinous process, in which it resembles the lumbar 

 vertebrae; and by each transverse process being subdivided into three elevations, 

 the superior, inferior, and lateral tubercles: the superior and inferior correspond 

 to the mammillary and accessory processes of the lumbar vertebrae. Traces of 

 similar elevations are found on the transverse processes of the tenth and eleventh 

 thoracic vertebras. 



Superior articular process 



FIG. 92. A lumbar vertebra seen from the side. 



The Lumbar Vertebrae (Vertebras Lumbales). 



The lumbar vertebrae (Figs. 92 and 93) are the largest segments of the movable 

 part of the vertebral column, and can be distinguished by the absence of a 

 foramen in the transverse process, and by the absence of facets on the sides of 

 the body. 



The body is large, wider from side to side than from before backward, and a 

 little thicker in front than behind. It is flattened or slightly concave above and 



