Til OR. I CIC RESPIR. t TI()\ 



31)5 



projjortioii o\' the hlooci collects that there is iiisudicient i)lo()(l to 

 lill the heart. 



III. Thoracic Respiration. The upper and lower regions of the 

 thorax should be considered separately. The muscles and move- 

 ments of the upper series of ribs are quite different from the lower 

 series. 



(a) Lower costal series (sixth to ninth or tenth rib). 



Tliis segment moves along with the diaphragm and leads to 

 the expansion downwards of the low^er lobes of the lungs. The 

 ribs are articulated to the spinal colunm 

 so that during inspiration the lateral and 

 anterior part of each moves outward more 

 than the one above it. Two movements 

 may be noted : 



(i.) The 50 to 70 mm. of each rib next 

 the spine to which is attached the erector 

 spinae muscle moves forward at each respira- 

 tion. The tubercle of the rib slides forw-ard 

 on the flat upper facet of the transverse 

 process. 



(ii.) The non-spinal portion of a pair of 

 ribs moves with a bucket-handle action, 

 rising and coming forward with each in- 

 spiration. At the centre of each pair is the 

 sternum-cartilage complex w^hich is raised 

 and forced forwards during inspiration. 

 The muscles concerned in this increase of 

 the volume of the lower thorax, trans- 

 versely and antero-posteriorly, are the 

 external intercostals. 



(b) Upper costal series (second to fifth 

 rib). 



These ribs differ from the lower series in 

 shape, articulation, ligamentation, musculature and, consequently, 

 in their movements. 



(i.) Shape. The upper ribs have a concave upper margin and 

 do not have such a marked twist as those in the lower costal 

 series. The second rib as a matter of fact may be laid flat on a 

 table. 



(ii.) Articulation. The spinal articulation differs from the lo\ver 

 series mainly in that the convex ovoid facet of the tubercle fits 

 into a corresponding cavity in the transverse process instead of 

 gliding on a flat facet. The costal articulations are nearly in a 

 transverse axis (Fig. 95), and movement occurs at the manubrio- 



— Rib and vertebra 

 in upper and in lower costal 

 series to sliow the difference 

 in the obliquity of articulation 

 and the resulting difference in 

 the expansion of the chest. 

 Note direction of arrows. 

 (From Noel Paten's " Essentials 

 of Human Physiology.") 



