ELEMENTAEY EXPERIMENTAL PHYSIOLOGY 89 



CHAPTER XXI. 

 INSPECTION AND AUSCULTATION OF THE THORAX. 



Inspection. The normal chest has the shape of a truncated cone. 

 It is well and symmetrically expanded ; the sternum and vertebral 

 column are erect, while the anterior wall of the thorax is slightly 

 arched forwards. The transverse section is oval, with the wider 

 diameter from side to side. The sub-costal angle is wide. Measure the 

 chest with a tape. The average measurement round the chest is 35 

 inches, or rather more than half the height of the man. With the 

 calipers measure the side to side diameter; it averages 10-10J inches at 

 the level of the nipple. The antero-posterior diameter is 7J inches on 

 the average. Measure the difference in the circumference between 

 the inspiratory and expiratory positions. It averages 2J-3J inches. 

 Take the shape of the chest with the cyrtometer. This consists of 

 two pieces of lead piping hinged by a piece of rubber tubing. The 

 cyrtometer is moulded round the circumference of the thorax, then 

 opened arid removed, to be again placed in position on a sheet of 

 paper. The shape is then traced on the paper with a pencil. 



Observe during respiration that the abdominal movements are most 

 marked in men. In children and women the movement of the upper 

 part of the chest is more noticeable. 



Inspiration. The distensile lungs follow at every point the inspira- 

 tory enlargement of the thorax, and air and blood enter the lungs in 

 increased volume. The vertical diameter of the thoracic cavity is 

 increased by the contraction of the diaphragm. This dome-shaped 

 muscular sheet flattens until the acute angle between the thoracic wall 

 and the diaphragm becomes an obtuse angle. The pull of the 

 diaphragm on the lower ribs is antagonised by the pressure of the 

 diaphragm on the abdominal contents. The quadratus lumborum 

 fixes the twelfth rib, while the serratus posticus pulls the last four 

 ribs backwards. The central tendon of the diaphragm is slung to the 

 pericardium, and scarcely varies in position. The movements of the 

 diaphragm may be observed in man by means of the Rontgen rays. 

 The antero-posterior and transverse diameters of the thorax are 

 enlarged by the external intercostal muscles, the intercartilaginous parts 

 of the internal intercostals, and the levatores costarum. The scalene 

 muscles fix the upper two ribs. By the elevation of the ribs the 

 sternum is thrown forwards, the spine backwards, and the thorax is 

 enlarged both from before backwards, and from side to side. 



