BIOLOGY AND HEALTH 



427 



Proper exercise should 



1. Be vigorous, continuous, and reasonably prolonged. For 



FIG. 136. Superficial muscles of trunk, shoulder and back viewed from 

 behind. A, external occipital protuberance; 1-1, trapezius muscles; l' oval 

 tendon between right and left trapezius; l' insertion of trapezius; B, summit 

 of shoulder (acronium); 2-2', lateral muscle and insertion; 3, sterno-mastoid; 

 4, deltoid; 5, infraspinatus; 6, teres minor; 7, teres major; 8, rhomboideus 

 major; 9, part of external oblique muscle of abdomen. (After Allen Thom- 

 son.) From Kellogg. 



example a brisk walk is one of the best of exercises, while a short 

 stroll or saunter does little good, though often mistaken for " ex- 

 ercise." 



