NATURAL THEOLOGY. 121 



pable perhaps of generating a firmer assurance 

 than what can arise from a divided attention.^ 



The ginglymus, or hinge-joint, does not it is 

 manifest, admit of a Hgament of the same kind 

 with that of the ball and socket-joint ; but it is 

 always fortified by the species of ligament of 

 which it does admit. The strong, firm, investing 

 membrane, above described, accompanies it in 

 every part ; and in particular joints, this mem- 

 brane, which is properly a ligament, is considera- 

 bly stronger on the sides than either before or 

 behind, in order that the convexities may play 

 true in their concavities, and not be subject to 

 slip sideways, which is the chief danger; for the 

 muscular tendons generally restrain the parts from 

 going further than they ought to go in the plane 

 of their motion. In the knee^ which is a joint of 

 this form, and of great importance, there are su- 

 peradded to the common provisions for the sta- 

 bility of the joint, two strong ligaments, which 

 cross each other — and cross each other in such a 

 manner, as to secure the joint from being dis- 

 placed in any assignable direction. "I think," 

 says Cheselden, "that the knee cannot be com- 

 pletely dislocated without breaking the cross liga- 



^ This ligament is absent in the orang-outang ; and in the lower 

 extremity of this animal, there are other points of resemblance to 

 the structure of the arm ; and certainly the use of the hinder ex- 

 tremity corresponds with this structure, since he grasps and swings 

 equally well with either extremity. 



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