224 



MOTION AND COORDINATION 



The next twelve vertebrae, in order below tbe cervical, 

 are known as the thoracic vertebrae. They form the back 

 part of the framework of the thorax and have little free- 

 dom of motion. The five vertebrae below the thoracic are 

 known as the lumbar vertebrae. These bones are large 

 and strong and admit of considerable motion. Below the 

 last lumbar vertebra is a wedge-shaped bone which has 

 the appearance of five vertebrae fused together. This 

 bone, known as the sacrum, connects with the large bones 

 which form the pelvic girdle. Attached to the lower end 

 of the sacrum is a group of from two to four small verte- 

 brae, more or less fused, called the coccyx. 



The Joining of the Vertebrae. A typical vertebra consists of a 

 heavy, disk-shaped portion in front, called the body, which is connected 



FIG. 99. Two views of a lumbar vertebra. A. From above. B. From 

 the side. i. Body. 2, 3, 4, 5. Projections from the neural arch. 



with a ring-like portion behind, called the neural arch. The body and 

 the neural arch together encircle a round opening which is a part of 

 the canal that contains the spinal cord (Fig. 99). From the neural 

 arch are seven bony projections, or processes, three of which serve for 

 the attachment of muscles and ligaments, while the other four, two 

 above and two below, are for the interlocking of the vertebrae with 

 each other. The separate vertebrae are joined together in the spinal 

 column, as follows : 



a. Between the bodies of adjacent vertebrae are disks of elastic carti- 

 lage. Each disk is about one fourth of an inch thick and is grown 



