THE HUMAN FRAME. 69 



6one but one, has what anatomists call a process, namely, 

 a projection somewhat similar in size and shape to a tooth ; 

 which too'th entering a corresponding hole or socket in the 

 bone above it, forms a pivot or axle, upon which that upper 

 bone, together with the head which it supports, turns freely 

 in a circle, and as far in the circle as the attached muscles 

 permit the head to turn. Thus are both motions perfect 

 without interfering with each other. When we nod the 

 head, we use the hinge-joint, which lies between the head 

 and the first bone of the neck. When we turn the head 

 round, we use the tenon and mortise, which runs between 

 the first bone of the neck and the second. 



We see the same contrivance and the same principle 

 employed in the frame or mounting of a telescope. It is 

 occasionally requisite that the object-end of the instrument 

 be moved up and down, as well as horizontally or equato- 

 rially. For the vertical motion, there is a hinge, upon which 

 the telescope plays ; for the horizontal or equatorial motion, 

 an axis upon which the telescope and the hinge turn to- 

 gether. And this is exactly the mechanism which is appli- 

 ed to the motion of the head ; nor will any one here doubt 

 of the existence of counsel and design, except it be by that 

 debility of mind which can trust to its own reasonings m 

 nothing. 



We may add, that it was, on another account, also expe- 

 dient that the motion of the head backward and forward 

 should be performed upon the upper surface of the first ver- 

 tebra ; for, if the first vertebra itself had bent forward, it 

 would have brought the spinal marrow, at the very begin- 

 ning of its course, upon the point of the tooth. 



II. Another mechanical contrivance, not unlike the last 

 in its object, but diflerent and original in its means, is seen 

 in what anatomists call the fore-arm — that is, in the arm 

 between the elbow and the wrist.* Here, for the perfect 



* Plate II., Fig. 2. a, the humerus ; the head, ^, is a portion 

 of a sphere, au-l exhibits an instance /^f the Hll and socket, or univfr- 



