56 



SPECIAL ANA TOMY OF THE SKELETON 



Twelfth Thoracic Vertebra. The twelfth thoracic vertebra has the same 

 general characters as the eleventh, but may be distinguished from it by the in- 

 ferior articular processes being convex and turned outward, like those of the 

 lumbar vertebrae; and by the fact that this vertebra resembles the lumbar vertebrae 

 in the general form of the body, laminae, and spinous process; and by the trans- 

 verse processes being shorter, and marked by three elevations, the superior, 

 inferior, and external tubercles, which correspond to the mammillary, accessory, 

 and transverse processes of the lumbar vertebrae. There is no facet on its 

 transverse process for the twelfth rib. 



The Lumbar Vertebrae (Vertebrae Lumbales) (Fig. 21). 



The lumbar vertebrae are the largest segments of the vertebral column, and can 

 at once be distinguished by the absence of the foramen in the transverse process, 

 the characteristic point of the cervical vertebrae, and by the absence of any articu- 

 lating facet on the side of the body, the distinguishing mark of the thoracic 

 vertebrae. 



Superior articular process. 



FIG. 21. Lumbar vertebra. 



Body. The body is large, and has a greater diameter from side to side than 

 from before backward, slightly thicker in front than behind, flattened or slightly 

 concave above and below, concave behind, and deeply constricted in front and at 

 the sides, presenting prominent margins, which afford a broad surface for the 

 support of the superincumbent weight. 



Pedicles. The pedicles are very strong, directed backward from the upper 

 part of the bodies; consequently, the inferior intervertebral notches are of con- 

 siderable depth. 



Laminae. The laminae are broad, short, and strong, and the vertebral foramen 

 triangular, larger than in the thoracic, smaller than in the cervical, region. 



Processes. Spinous Processes. The spinous processes are thick and broad, 

 somewhat quadrilateral, horizontal in direction, thicker below than above, and 

 terminating in a rough, uneven border. 



Articular Processes. The superior articular processes are concave, and look 

 backward and inward; the inferior are convex, and look forward and outward; 

 the former are separated by a much wider interval than the latter, embracing 

 the lower articulating processes of the vertebra above. 



Transverse Processes. The transverse processes are long, slender, directed 

 transversely outward in the upper three lumbar vertebrae, slanting a little upward 

 in the lower two. They are situated in front of the articular processes, instead 



