THE RESPIRATORY SYSTEM 137 



knees with his hands, and so fix his fore-limbs; a patient 

 with embarrassed respiration will grasp the back of a 

 chair, or adopt any convenient hold which may make 

 him functionally a quadruped for the time being. 

 Arboreal life has done this for the Primate stock it has 

 given them flat chests and flat backs, has brought about 

 a greater degree of dependence upon the diaphragm as 

 a mechanism of inspiration, and at the same time, has 

 added to the mobile fore-limb an increased source of 

 mobility in the muscles of the external respiratory 

 system. 



