BONE EBGIONS 



Bone regions. — On the top of 

 this long, curved spinal column 

 is mounted a box-shaped collec- 

 tion of bony plates which is 

 called the skull. This box in- 

 closes the delicate brain and 

 forms the framework of the face. 

 The chest, or thorax, is formed 

 by a series of long, curved, flat 

 bones called the ribs, which curve 

 from the vertebrte at the back 

 around to the front of the body. 

 Here, they are united to a flat 

 structure, half bone, half gristle, 

 called the breastbone. This ar- 

 rangement secures the protec- 

 tion of the heart and lungs. 

 The abdominal cavity of the 

 body has no side walls of bone, 

 but at the bottom the soft parts 

 are supported by a basket-shaped 

 collection of bones connected to 

 the lower end of the spinal 

 column and known as the pelvis. 

 Finally, the arms and legs contain 

 a central axis of bones, which, in 

 the case of the arms, are con- 

 nected to the spinal column by 

 a girdle known as the shoulder 

 or pectoral girdle, and, in the 

 case of the legs, by the pelvic 

 bones or pelvic girdle. The 



i SPINAL 

 COLUMN 



Fig. S3 



