PHYSIOLOGY FOR BEGINNERS 



wards and forwards to the rib below. When the fibres passing 

 ,from the first rib to the second rib contract, the second rib is 

 drawn upwards towards the first rib, the first rib being pre- 

 vented from being drawn downwards by structures above it, and 



when necessary by the action 



/*""" "~\ r ,..v of the scalene muscles 



* A--'"' which pass from the cervical 



vertebra? down to the first 

 and second ribs in front. Sim- 

 ilarly the external intercostal 

 muscles between the second 

 -fr 7 and third ribs draw the third 

 rib upwards towards the 

 second, and so on for the 

 succeeding ribs. All the 

 external intercostal muscles 

 contract at the same time, 

 and thus all the ribs are 



FIG. 56. Diagram to show the movements raised towards the first, the 



of the ribs and sternum in inspiration. j Qwer Qnes moving upwa rds 



rs.re.^.slh.eth.andyihribs^verte- most , n ^ ^ 



bral column; s, sternum; c, cartilages. . * 



The dotted lines show the position of the sternum, especially its lower 

 ribs and sternum at inspiration. end, is carried upwards and 



thrust forwards. Look at the 



chest of a boy sideways ; you will see this movement of the 

 sternum taking place, giving an increase in the size of the 

 chest from behind forwards with each inspiration. 



Look at the chest of a boy from the front ; you will 

 see that, with each inspiration, the chest, especially the lower 

 part, increases in width from side to side. This you can dis- 

 tinctly see is caused by the arches of the lower ribs, especially 

 of the seventh, eighth, and ninth, which are united together 

 by their cartilages to form the prominent lower limit of the 

 framework of the chest, moving outwards. For not only do 

 the ribs slant so that their sternal ends are on a lower level 

 than their vertebral ends, but they sag in the middle of their 

 curvature, so that the middle of the arch does not prop out the 

 wall of the chest as much as it would if it had not, as it were, 

 dropped away. When the external intercostal muscles contract 

 this middle part of each rib is especially raised, and so the 



