IN THE HUMAN FRAME, 63 



space within the chest by the flattening or descent of the 

 diaphram, leaves room for forty-two cubic inches of air to 

 enter at every drawing in of tlie breath. When there is a 

 necessity for a deeper and more laborious inspiration, the 

 enlargement of the capacity of the chest may be so increas- 

 ed by effort, as that the lungs may be distended with seventy 

 or a hundred such cubic inches,* The thorax, says Schel- 

 hammer, forms a kind of bellows,'such as never have been^ 

 nor probably will be made by any artificer.! 



*Anat. p. 229. 



t The thorax, or chest, is composed of bones and cartilages, so dis^ 

 posed as to sustain and protect the most vital parts, the heart and 

 lungs, and to turn and twist with perfect faciUty in every motion of 

 the body ; and to be in incessant motion in the act of respiration, without 

 a moment's interval during a whole life. In anatomical description, 

 the thorax is formed of the vertebral column, or spine, on the back 

 part, the ribs on either side, and the breast bone, or sternum, on the 

 fore part. But the thing most to be admired is the manner in which 

 these bones are united, and especially the manner in which the ribs 

 are joined to the breast bone, by the interposition of cartilages, or gris- 

 tle, of a substance softer than bone, and more elastic and yielding. By 

 this quality they are fitted for protecting the chest against the effects 

 of violence, and even for sustaining life after the muscular power of 

 respiration has become too feeble to continue without this support. 



If the ribs were complete circles, formed of bone, and extending 

 from the spine to the breast bone, life would be endangered by any 

 accidental fracture ; and even the rubs and jolts to which the human 

 frame is continually exposed, would be too much for their delicate and 

 brittle texture. But these evils are avoided by the interposition of the 

 elastic cartilage. On their forepart the ribs are eked out, and joined to 

 the breast bone by means of cartilages, of a form corresponding to that 

 of the ribs, being, as it were, a completion of the arch of the rib, by 

 a substance more adapted to yield in every shock or motion of the 

 body. The elasticity of this portion subdues those shocks which would 

 occasion the breaking of the ribs. We lean forward, or to one side, 

 and the ribs accommodate themselves, not by a change of form in the 

 bones, but by the bending or elasticity of the cartilages. A severe 

 blow upon the ribs does not break them, because their extremities re- 

 coil and yield to the violence. It is only in youth, however, when 

 the human frame is in perfection, that this pliancy and elasticity have 

 full effect. When old age approaches, the cartilages of the ribs 

 become bony. They attach themselves firmly to the breast-bone, 

 and the extremities of the ribs are fixed, as if the whole arch were 

 formed of bone unyielding and inelastic. Then every violent blow 

 upon the side is attended with fracture of the rib, an accident seldom 

 occurring in childhood, or in youth. 



But there is a purpose still more important to be accomplished by 

 means of the elastic structure of the ribs, as partly formed of cartil- 

 age. This is in the action of breathing, or respiration ; especially in 

 the more highly-raised respiration which is necessary in great ex- 

 ertions of bodily strength, and in>iolent exercise. There are two acts 

 of breathing — expiration, or the sending forth of the breath ; and in- 



