THE SKELETON AND MUSCLES 



331 



The vertebral column (fig. 166). — ^The long backbone 

 in man is composed of separate ringlike pieces, called verte- 

 bra, placed one above the other. Each has several lateral pro- 

 jections for the attachment of muscles and for interlocking 



adjacent vertebrae. 

 The vertebrae are 

 held together by 

 strong ligaments, 

 passing from one ver- 

 tebra to another. The 

 first seven vertebrae 

 are called cervical or 

 neck vertebrae. The 

 next twelve are the 

 dorsal vertebrae. To 

 each one of these is 

 attached a pair of 

 ribs, as shown in fig. 

 167. The last five 

 are the lumbar ver- 

 tebrae. The single 

 large bone below the 

 lumbar vertebrae is 

 the sacrum and the 

 curved tip at the end 

 is the coccyx. The 

 sacrum is really com- 

 posed of five vertebras 



Fig. 167. Lower half of thorax with dorsal 

 and lumbar vertebrae. A, sixth dorsal 

 vertebrae; Ac, aorta; D, (lower) dia- 

 phragm; D, (upper) aorta passing through 

 diaphragm; I, intercostal muscles; O, 

 oesophagus; IV, opening in diaphragm for 

 vena cava ascending; T T, tendons of 

 right and left crura attaching diaphragm 

 to 3rd, and 4th lumbar vertebree. (After 

 Allen Thomson.) 



fused together, and the coccyx of four bones fused into one. 

 Each of the twenty-six vertebrae differs a little in shape 

 from its neighbor, but all are nicely adjusted to one another. 



Between the vertebras are pads of elastic cartilage. These 

 act as cushions and prevent jarring of the vertebral column. 



The ribs. — The ribs, articulating with the twelve dorsal 

 vertebrae, are held in place by sheaths of connecting muscles 



