20 EVOLUTION, OLD AND NEW. 



a sinus or cliff into two heads or protubarances ; and 

 these heads on the back part stand out beyond the 

 cylinder of the bone. Through the hollow which lies 

 between the hind parts of these two heads, that is to 

 say, under the ham, between the ham strings, and 

 within the concave recess of the bone formed by the 

 extuberances on either side ; in a word, along a defile 

 between rocks pass the great vessels and nerves which 

 go to the leg. Who led these vessels by a road so 

 defended and secured ? In the joint at the shoulder, 

 in the edge of the cup which receives the head of the 

 bone, is a notch which is covered at the top with a 

 ligament. Through this hole thus guarded the blood- 

 vessels steal to their destination in the arm instead of 

 mounting over the edge of the concavity." * 



****** 



"What contrivance can be more mechanical than 

 the following, viz. : a slit in one tendon to let another 

 tendon pass through it ? This structure is found in the 

 tendons which move the toes and fingers. The long 

 tendon, as it is called in the foot, which bends the first 

 joint of the toe, passes through the short tendon which 

 bends the second joint ; which course allows to the 

 sinews more liberty and a more commodious action 

 than it would otherwise have been capable of exerting. 

 There is nothing, I believe, in a silk or cotton mill, in 

 the belts or straps or ropes by which the motion is 

 communicated from one part of the machine to another 

 that is more artificial, or more evidently so, than this 

 perforation. 



" The next circumstance which I shall mention under 

 * * Natural Theology,' ch. viii. 



