102 NATURAL THEOLOGY. 



existence of counsel and design, except it be by 

 that debility of mind, which can trust to its own 

 reasonings in nothing. 



We may add, that it was, on another account, 

 also expedient that the motion of the head back- 

 ward and forward should be performed upon the 

 upper surface of the first vertebra ; for, if the first 

 vertebra itself had bent forward, it would have 

 brought the spinal marrov/, at the very beginning 

 of its course, upon the point of the tooth. 



II. Another mechanical contrivance, not unlike 

 the last in its object, but difterent and original in its 

 means, is seen in what anatomists call the frre-arm — 

 that is, in the arm between the elbow and the wrist. 

 Here, for the perfect use of the limb, two motions 

 are w^anted : a motion at the elbow, backward and 

 forward, which is called a reciprocal motion ; and 

 a rotatory motion, by w^hich the palm of the hand, 

 as occasion requires, may be turned upward. 

 How is this managed ? The fore-arm, it is well 

 known, consists of two bones, lying alongside each 

 other, but touching only towards the ends. One, 

 and only one, of these bones is joined to the cubit, 

 or upper part of the arm, at the elbow ; the other 

 alone to the hand at the wrist. The first, by 

 means, at the elbow, of a hinge-joint (which allows 

 only of motion in the same plane,) swings back- 

 ward and forward, carrying along with it the other 

 bone, and the whole fore-arm. In the meantime, 

 as often as there is occasion to turn the palm up- 

 ward, that other bone to which the hand is at- 



