PHYSIOLOGY FOR BEGINNERS 



attached in front to the sternum and to the cartilages of the 

 ribs which meet the lower end of the sternum, at the sides 

 to the lower ribs, and at the back by two particularly strong 

 bands, called the pillars of the diaphragm, to the bodies 

 of the lumbar vertebra?. The muscular portion of the dia- 

 phragm, like other muscular tissue, is capable of contraction, 

 and when this takes place the parts to which the diaphragm is 

 attached are not moved, but the muscular portion pulls on the 



FIG. 54. -Tlie diaphragm viewed from the abdomen. 



The central tendinous part is more lightly shaded than the outer muscular part. The 

 following structures passing through the diaphragm are shown cut across : 

 Ao, aorta ; TAD, thoracic duct ; V.C.I, inferior vena cava ; (, ixsopliagus. 



central tendinous portion, and drawing this down causes the 

 arch of the diaphragm to become less convex. This increases 

 the thoracic cavity from above downwards. 



The Movements of the Bibs and Sternum Inspira- 

 tion. The ribs, sweeping round from the vertebral column 

 behind to the sternum in front, form with the intercostal 

 muscles between them the lateral walls of the chest. The ribs 

 do not proceed horizontally round the wall of the chest, but 

 slope obliquely downwards as they proceed forwards from the 

 back. The first rib forms the smallest arch, and the arch 

 of each increases as we pass downwards to the last of them, 

 the seventh, which meets the sternum. Each rib is articulated, 



