40 PHYSIOLOGY. 



4. Every joint is enclosed by a firm fibrous bag, called 

 the capsidar ligament, the internal surface of which secretes a 

 fluid, termed synovia, which lubricates the joints, and serves 

 the same purpose that oil does in a piece of machiner>\ . At 

 the wrist and ankle, and along the fingers and toes, the liga- 

 ments form strong bandages to bi'nd down the muscles and 

 tendons, and enables them to act with greater precision and 

 steadiness ; otherwise when the muscle contracted, the ten- 

 dons would start out like the string of a bow, and thus not 

 only destroy the symmetry of the parts, but entirely prevent 

 motion, When sprained by over exertion or accident, an 

 artificial bandage becomes ncccssar^; we then find how su- 

 perior the natural ligaments are to any artificial bandage that 

 can be contrived. 



5. Tendon or Sinew. This well-known structure is 

 plainly perceptible(at the wrist, on the back of the hand, at 

 the heel, &c. (They have a white, pearly lustre, possess 

 great strength, but little elasticity. They are composed 

 of bundles of parallel threads, bound * together by trans- 

 verse threads, and they vary both in figure and extent ; some 

 being cylindrical and tapering to the point of insertion, 

 and in others forming broad expansions., So insensible are 

 tendons, that when ruptured, as the tendon of Achilles at the 

 heel, not the slightest pain is felt, but the person feels that he 

 has received a smart blow, or that a part of the floor has given 

 way under him.^ 



0. Where force is to be exerted upon some distinct point, it 

 is transmitted along a tendon, as forces in machinery are by 

 ropes?* When a tendon passes over a joint, a bone is formed 

 sometimes where it crosses, as the knee-pan in front of the 

 knee joint ; which is a bone placed directly in the centre of 

 the tendon, and (serves, to throw the force farther -from the 

 centre of motion, thereby increasing the lever, and conse- 

 quently the effect.) Similar bones are often found in the 

 tendons of the feet. 



