134 NATURAL THEOLOGY. 



of the muscles, by the aid of a considerable and 

 equipolent muscular force in constant exertion, that 

 the head maintains its erect posture. The muscles 

 here supply what would otherwise be a great de- 

 fect in the articulation ; for the joint in the neck, 

 although admirably adapted to the motion of the 

 head, is insufficient for its support. It is not only 

 by the means of a most curious structure of the 

 bones that a man turns his head, but by virtue of 

 an adjusted muscular power that he even holds 

 it up. 



As another example of what we are illustrating, 

 viz., conformity of use between the bones and the 

 muscles, it has been observed of the diiferent ver- 

 tebra?, that their processes are exactly proportioned 

 to the quantity of motion which the other bones al- 

 low of, and which the respective muscles are capa- 

 ble of producing. 



II. A muscle acts only by contraction. Its force 

 is exerted in no other way. When the -exertion 

 ceases, it relaxes itself; that is, it returns by relaxa- 

 tion to its former state, but without energy.^* This 



3* Excellently well as this is put, there is something more admi- 

 rable still in the condition of the muscular system. With respect 

 to the S'lpport of the head, as mentioned in the preceding page, and 

 the instance embraces, of course, the erect position of the body as 

 well as the equable poising of the head, the most extraordinary part 

 of the plienomenon is this, that we are sensible of the slightest in- 

 clination of the body or of any member, although it would be diffi- 

 cult to say to what order of acknowledged sensations this belongs. 

 Not onlv do we feel every degree of inclination from the perpen- 

 dicular in the poising of the body, but we act upon it with the most 



