NATURAL THEOLOGY. 115 



tening or descent of the diaphragm, leaves room 

 for forty-two cubic inches of air to enter at every 

 drawing-in of the breath. When there is a neces- 

 sity for a deeper and more laborious inspiration, 

 the enlargement of the capacity of the chest may 

 be so increased by efibrt, as that the lungs may 

 be distended with seventy or a hundred such 

 cubic inches.* The thorax, says Schelhammer, 

 forms a kind of bellows, such as never have been, 

 nor probably will be, made by any artificer.^ 



V. The patella, or knee-pan, is a curious little 

 bone : in its form and office unlike any other bone 

 in the body. It is circular; the size of a crown- 

 piece ; pretty thick ; a little convex on both sides, 

 and covered with a smooth cartilage. It lies 

 upon the front of the knee: and the powerful 

 tendons, by which the leg is brought forward, 

 pass through it (or rather it makes a part of their 

 continuation,) from their origin in the thigh to 

 their insertion in the tibia. It protects both the 

 tendon and the joint from any injury which either 

 might suffer, by the rubbing of one against the 

 other, or by the pressure of unequal surfaces. It 

 also gives to the tendons a very considerable me- 

 chanical advantage, by altering the line of their 



2' In the dissertation in the Appendix on the Thorax, it will be 

 observed that we have additional proofs of the accommodation of 

 the bones of the trunk, as well as of the bones of the extremities, 

 to the varying habits and condition of the animal. 



* Anat. p. 229. 



