30 THE HUMAN BODY. 



The vertebral column. (Fig. 9.) The upper portion 

 of the spine consists of twenty-four separate bones, each 

 called a vertebra; these are piled one above the other, and 

 separated by elastic pads made of cartilage and connective 

 tissue. Seven vertebrae (cervical, C 1-7) are found in the 

 neck ; twelve (dorsal, D 1-12) lie at the back of the chest 

 and carry the ribs ; and five (lumbar, L 1-5) are in the 

 loins. 



Below the separate vertebrae comes the sacrum, (S 1), 

 which is shown as seen from its ventral aspect in Fig. 10, 

 along with the lowest lumbar vertebra. In childhood the 

 sacrum consists of five distinct vertebrae, but these grow 

 together afterwards, though cross ridges remain indicating 

 the original lines of separation. Succeeding the sacrum 

 and forming the lower end of the spine is the coccyx (Co, 

 1-4, Fig. 9), a single bone in adults, though consisting of 

 four pieces in children. 



The structure of a vertebra. Those vertebrae which 

 remain permanently separate resemble one another in 

 general form, with the exception of the uppermost two. 

 As an example we may take the eleventh from the skull, 

 that is the fourth dorsal vertebra (Figs. 11 and 12). 



In it we find (1) a thick bony mass, C, rounded on the 

 sides and flattened above and below where it is turned 

 toward its neighbors ; this part is the centrum or body of 



Of what is the upper portion of the backbone composed? What 

 .are the bones forming it called? What lies between them? How 

 many vertebrae in the neck ? In the chest region? In the loins? 



Of what parts is the lower portion of the vertebral column com- 

 posed? How many vertebrae form the sacrum? At what period of 

 life are they separate? How is this original separation indicated on 

 the sacrum of adults? How many vertebrae are united to form the 

 coccyx? 



What vertebrae differ essentially in form from the rest? Describe 

 a typical vertebra. 



