NATURAL THEOLOGY. 79 



more than twenty bones. But one exception was 

 necessary to enable the head to turn, by a motion of 

 its own, without always being at the trouble of turn- 

 ing the whole body. To admit of this, one solitary 

 deviation is introduced. One bone of the neck, which 

 is a part of the spine, is permitted to turn round, 

 and only one. The construction is tljis. The head, 

 together with the first bone of the neck, forms a per- 

 fect swivel, like the head of a cane, made to twirl 

 round upon the staff. There is a notch in the first 

 bone which receives a pin that runs up into it from 

 the second, making what mechanics would call a. pin, 

 or pivot joint. Upon this joint the head has a firm 

 and accurate motion within a certain extent on each 

 side, as far as is necessary. 



B. Every part seems to be the most wonderful, 

 till we hear another described. Still, one might al- 

 most tremble to think of turning the neck, after what 

 anatomists say of the spinal marrow. 



T. It is this which renders the mechanism truly 

 remarkable. There was plainly a choice of joints to 

 enable the head to turn. Now, anatomists invite our 

 attention to the singular safety of the joint by which 

 this motion is performed. 



A. There are several joints which would have 

 permitted it. The bone which revolves might have 

 been fitted with a cavity to the head of the bone im- 

 mediately beneath. There are a number of these 

 joints in the body. They are called ball and socket 

 joints, in which the head of one bone is received into 

 a cup or socket in the other. There is such a joint 



