SKELETON. 381 



having a number of joints or movements [of parts of the skeleton] on 

 each other, have so many fixed points ; the larger portion becoming the 

 fixed point to the smaller ; until, at last, the whole body has its fixed 

 point, or point of resistance to move upon. Animals that move upon 

 the earth, have that for their fixed point ; birds that fly have the air 

 for their fixed point ; and fishes have the water for their fixed point. 



Besides these general fixed points of motion for the whole animal, 

 each animal has a fixed point within itself from which the parts of the 

 body take their principal motion. In the human body this fixed point 

 seems to be in the joints of the thigh-bones ; and being in the middle 

 of the body, it must be common to the extremities ; therefore we see 

 that the trunk either moves on the legs, or the legs on the trunk. 

 Besides this there are as many fixed points as there are joints ; so that 

 the body is to be looked upon as a chain of joints whose general centre 

 of motion is in the joints of the thighs ; but each has its centre of motion, 

 which is always on that side next to the general. 



The greater the motion in any joint, the less nice it is ; therefore, 

 where correctness and nicety is wanted, the parts of motion are divided 

 into smaller movements ; as, for instance, the bones of the fingers become 

 shorter and shorter towards their terminations. 



Of the Spine. — The spine in animals is that which is the basis of the 

 whole body, on which everything is built. It gives support to the 

 whole, and may be said to be like the keel of a ship — the first thing 

 laid down, from which the whole superstructure is to arise. Prom its 

 great length, it is necessary to have motion within itself; and, as it 

 would be improper for it to bend at one part sufficiently for the required 

 motion, more especially on account of the ribs and viscera, it is made 

 up of a number of bones, that it might have an easy motion through 

 the whole : this also protects the spinal marrow from being hurt by too 

 quick a bend. 



The other joints have no parts save for their simple motion ; but the 

 trunk has a great many, which prevents such motion. 



The spine is straight in a fore view, because the two sides of the body 

 are similar parts ; but the back and fore parts not being similar, the 

 spine is bent accordingly, to be able to support the different weights 

 applied to it. However, this is observable principally in the human 

 subject, owing to his erect position. -That part of the spine to which 

 the other bones of the pelvis are attached [the sacrum], is commonly 

 nearly in the same line with the rest of the chain of bones ; although, 

 in most, it is a little bent so as to give space to the pelvis ; but in the 

 human it is thrown further back, in order that the thigh-bones might 

 be brought perpendicularly under the spine, and at the same time the 



