114 NATURAL THEOLOGY. 



same properties, is but a bungling piece of work- 

 manship in comparison witli that of which we 

 speak. 



lY. The reciprocal enlargement and contrac- 

 tion of the chest to allow for the play of the lungs, 

 depends upon a simple yet beautiful mechanical 

 contrivance, referable to the structure of the bones 

 which enclose it. The ribs are articulated to the 

 back-bone, or rather to its side projections, oh- 

 liquely : that is, in their natural position they 

 bend or slope from the place of articulation down- 

 wards. But the basis upon which they rest at 

 this end being fixed, the consequence of the obli- 

 quity, or the inclination downwards, is, that when 

 they come to move, whatever pulls the ribs up- 

 wards, necessarily, at the same time, draws them 

 out; and that, whilst the ribs are brought to a 

 right angle with the spine behind, the sternum, or 

 part of the chest to which they are attached in 

 front, is thrust forward. The simple action, there- 

 fore, of the elevating muscles does the business; 

 whereas, if the ribs had been articulated with the 

 bodies of the vertebrae at right angles, the cavity 

 of the thorax could never have been further en- 

 larged by a change of their position. If each rib 

 had been a rigid bone, articulated at both ends to 

 fixed bases, the whole chest had been immov- 

 able. Keill has observed that the breast-bone, in 

 an easy inspiration, is thrust out one-tenth of an 

 inch; and he calculates that this, added to what 

 is gained to the space within the chest by the flat- 



