NATURAL THEOLOGY. 161 



parapets on each side, which last description is re- 

 markable in the bones of the fingers, these being 

 hollowed out, on the under side, like a scoop, and 

 with such a concavity, that the finger may be cut 

 across to the bone, without hurting the artery which 

 runs along it. At other times, the arteries pass in 

 canals wrought in the substance, and in the very 

 middle of the substance, of the bone. This takes 

 place in the lower jaw ; and is found w^here there 

 would, otherwise, be danger of compression by 

 sudden curvature. All this care is wonderful, yet 

 not more than what the importance of the case re- 

 quired. To those who venture their lives in a ship, 

 it has been often said, that there is only an inch- 

 board between them and death ; but in the body 

 itself, especially in the arterial system, there is, in 

 many parts, only a membrane, a skin, a thread. 

 For which reason, this system lies deep under the 

 integuments ; wiiereas the veins, in which the mis- 

 chief that ensues from injuring the coats is much 

 less, lie in general above the arteries ; come nearer 

 to the surface ; are more exposed. 



It may be further observed concerning the two 

 systems taken together, that though the arterial, 

 with its trunk and branches and small twigs, may 

 be imagined to issue or proceed — in other words, 

 to grow, from the heart, like a plant from its root, 

 or the fibres of a leaf from its foot-stalk (which 

 however, were it so, would be only to resolve one 

 mechanism into another,) yet the venal, the re- 

 turning system, can never be formed in this man- 



14* 



