148 NATURAL THEOLOGY. 



nical, IS not the only thing in sphincters which 

 deserves our notice. The regulated degree of 

 contractile force with which they are endowed, 

 sufficient for retention, yet vincible w^hen requisite, 

 together with their ordinary state of actual con- 

 traction, by means of which their dependence 

 upon the will is not constant but occasional, gives 

 to them a constitution of which the conveniency 

 is inestimable. This their semi-voluntary charac- 

 ter is exactly such as suits with the wants and 

 functions of the animal. 



III. We may also, upon the subject of muscles, 

 observe, that many of our most important actions 

 are achieved by the combined help of different 

 muscles. Frequently, a diagonal motion is pro- 

 duced by the contraction of tendons pulling in the 

 direction of the sides of the parallelogram. This 

 is the case, as hath been already notice'd, with 

 some of the oblique nutations of the head. Some- 

 times the number of co-operating muscles is very 

 great. Dr. Nieuentyt, in the Leipsic Transactions, 

 reckons up a hundred muscles that are employed 

 every time we breathe ; yet we take in, or let out, 

 our breath, without reflecting w^hat a work is 

 thereby performed ; what an apparatus is laid in 

 of instruments for the service, and how many such 

 contribute their assistance to the effect. Breath- 

 ins with ease is a blessinor of every moment ; vet 

 of all others it is that which we possess with 

 the least consciousness. A man in an asthma is 

 the only man who knows how to estimate it. 



