RESPIRATION. 



349 



In ascending, the ribs straighten upon the spinal column, and, 

 instead of the lower ones in particular being so oblique, are now 

 found to occupy a more nearly horizontal plane. This increases the 

 antero-posterior diameter. At the same time that the ribs are raised 

 they undergo a movement of rotation, by virtue of which they sep- 

 arate from the median line of the chest. It is this movement which 

 produces an enlargement of the thorax in its lateral diameter at the 

 same time the antero-posterior diameter is slightly increased. 





Fig. 120. Schema of Action of Intercostal Muscles. (LANDOIS.) 



I. When the rods a and & which represent the ribs are raised, the inter- 

 costal space must be widened (e, f c, d). On the opposite side when the 

 rods are raised the line g-h is shortened (i, k g, h), the direction of the 

 external intercostal, l-m, is lengthened (I, m o, n) in the direction of the 

 (internal intercostals. 



II. When the ribs are raised the intercartilaginei indicated by g-Ji and the 

 external intercostals indicated by l-k are shortened. When the ribs are raised 

 the position of the muscular fibers is indicated by the diagonals of the rhombs 

 becoming shorter. 



During extraordinary inspiration as that caused by violent 

 muscular exercise or when some pathological condition is present so 

 that air finds its way into the chest only as the result of strong mus- 

 cular effort the other muscles are called into service: the scaleni, 

 sterno-cleido mastoids, trapezii, lesser pectorals, posterior serrati, 



