THE BONES AND JOINTS. 



21 



3, The spine in a baby is perfectly straight, and his 

 back flat. As he grows and walks the spine becomes 

 slightly curved backward in the region of the shoulder- 

 blades, and forward at the waist. This is natural. But 

 frequently the curve of the back becomes too great. The 

 shoulders are drawn forward, and the chest flattened. 

 This makes a stoop. It is caused by weakness of the 

 muscles which sustain the back and head, or indolence 

 and carelessness. It makes an ungraceful shape, and is 

 injurious because it compresses the heart and lungs, and 

 checks their free action. An erect posture and a full 

 chest should be cultivated. To this end, the muscles of 

 the chest and trunk must be kept vigorous by exercise. 



1st rib. 



Clavicle. 



False ribs. 



Fig. 5. THE THORAX. 



The natural curves of the spine are forward and back- 

 ward. A curve to one side is unnatural and a deformity. 

 It comes from bodily weakness, lack of air and exercise, 



