THE SKELETON. 335 



Articulations of a Vertebra. The smooth places where 

 the articulating processes join are called facets. Observe 

 on each side of the body of the vertebra a facet where the 

 head of the rib articulated. There is also a facet on the 

 transverse process where the tubercle of the rib articulated. 



The Cervical Vertebrae. The seven cervical vertebrae 

 (neck) have holes through their sides, or transverse pro- 

 cesses, for the passage of blood tubes. 



Atlas and Axis. The first vertebra, the atlas, has no 

 body. The second vertebra is the axis. It has a peg, 

 called the odontoid process, which represents the body of 

 the atlas. In shaking the head, the atlas, with the head, 

 turns on the axis. In nodding the head, the head simply 

 rocks back and forth on the atlas. 



The Thoracic Vertebrae. The twelve rib-supporting 

 vertebrae are the thoracic vertebrae. 



The Lumbar Vertebrae. The next five are the lumbar. 



The Sacrum and Coccyx. The sacrum is composed of 

 five vertebrae grown together, and the remaining four are 

 combined in the coccyx. 



Review of the Spinal Column. Let the eye slowly 

 review the whole spinal column, noting what the vertebrae 

 have in common. Note also their differences. 



Flexibility of the Spinal Column. In most articulated 

 skeletons there are pads of felt between the vertebrae. 

 These take the place of the inter-vertebral cartilages, 

 which are a form of connective tissue, possessing the elas- 

 ticity of cartilage and the toughness of fibrous connective 

 tissue, such as ligament and tendon. These inter-vertebral 



