88 NATURAL THEOLOaY. 



the bones for the rotary motions of the head and hands : 

 there is, also, in the oblique direction of the muscles belong- 

 ing to them, a specific provision for the putting of tliis mech- 

 anism of the bones into action. And mark the consent of 

 uses : the oblique muscles would have been inefficient with- 

 out that particular articulation ; that particular articulation 

 would have been lost v/ithout the oblique miuscles. It may 

 be proper, however, to observe, with respect to the head, 

 although I think it does not vary the case, that its oblique 

 motions and inclinations are often motions in a diagonal. 

 produced by the joint action of muscles lying in straight di- 

 rections. But whether the pull be single or combined, the 

 articulation is always such as to be capable of obeying the 

 action of the muscles. The oblique muscles attached to the 

 head are likewise so disposed as to be capable of steadying 

 the globe, as well as of moving it. The head of a new-born 

 infant is often obliged to be filleted up. After death, the 

 head drops and rolls in every direction. So that it is by the 

 equihbre of the muscles, by the aid of a considerable and 

 equipollent mu3cular force in constant exertion, that the 

 head maintains its erect posture. The muscles here supply 

 what would otherwise be a great defect 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 liot 

 only by the means of a most curious structure of the bones 

 that a man turns his head, but by virtue of an adjusted mus- 

 cular power that he even holds it up. 



As another exanrple of what we are illustrating, namely, 

 conformity of use between the bones and the muscles, it has 

 been observed of the different vertebra3, that their processes 

 are exactly proportioned to the quantity of motion which the 

 other bones allow of, and which the respective muscles are 

 capable of producing. 



II. A muscle acts only by contraction. Its force is exert- 

 ed in no other way. When the exertion ceases, it relaxes 

 itself: that is, it returns by relaxation to its former state. 



