16 STRUCTURE OF THE HUMAN BODY 



Sacrum. Below the lumbar region, the greatest 

 strength and stability are required because the weight of 

 the trunk is here "transmitted through the hip bones 

 to the legs. Five of the vertebral bones are therefore 

 united to form a single broad strong bone, the sacrum. 



Coccyx. Below the sacrum are several small bones- 

 which constitute the coccyx. They are the sole remnant 

 of a possible prehistoric tail and owing to their exposed 

 position are somewhat frequently injured. 



Flexibility of spine. As we have seen, the vertebra* 

 form a series of short branching bones knit together by 

 ligaments into the spinal column. The movement per- 



Front ligamen 



Back ligamen 



Body of verteb 

 Spine of vertebra 



Intervertebral discs 

 of elastic:cartt 



Canal for spinal cord 



FIG. 12. A section through three vertabrae, showing structure of bone and 

 arrangement of ligaments. 



mitted between each pair of vertebrae is slight and the 

 ligaments which bind them together are strong. As a 

 result, the spinal column is firm. Its flexibility is not sac- 

 rificed, however, because there are so many joints that 

 a slight movement on the part of each results in a con- 

 siderable curve of the whole 



