74 OF THE MUSCLES. 



Moveable joints, I think, compose tiie curiosity of bones ; 

 but their union, even where no motion is intended or want- 

 ed carries marks of mechanism and of mechanical wis- 

 dom. The teeth, especially the front teeth, are one 

 bone fixed in another like a peg driven into a board. The 

 sutures of the skull are like the edges of two saws clapp- 

 ed together, in such a manner as that the teeth of one 

 enter the intervals of the other.* We have sometimes one 

 bone lapping over another, and planed down at the edges ; 

 sometimes also the thin lamella of one bone received into 

 a narrow furrow of another. In all which varieties we 

 seem to discover the same design, viz. firmness of juncture, 

 without clumsiness in the seam. 



CHAP. IX. 



OF THE MUSCLES. 



Muscles, with their tendons, are the instruments by 

 which animal motion is performed. It will be our business 

 to point out instances in which, and properties with respect 

 to which, the disposition of these muscles is as strictly 

 mechanical, as that of the wires and strings of a puppet.t 



* Most of the bones of the skull are composed of two plates or tob- 

 lets, with an intermediate spongy, vascular substance ; the outer tablet 

 is fibroua, having the edges curiously indented and united by a dove- 

 tailed suture ; the inner from its brittleness is called vitreous, and 

 therefore merely joined together in a straight line ; this mode of union 

 is not accidental — not the result of chance, but design. The author of 

 the treatise on "Animal Mechanics" gives the following admirable il- 

 lusti-ation of the structure : — 



*' Suppose a carpenter employed upon his own material — he would 

 join a box with regular indentations by dove-tailing, because he knows 

 that the material on which he works, from its softness and toughness, 

 admits of such adjustment of its edges. The processes of bone shoot 

 into the opposite cavities with an exact resemblance to the fox-tail 

 wedge of the carpenter. 



" But if a workman in glass or marble were to join these materials, 

 he would smooth the edges and unite them by cement; for if he could 

 succeed in indenting the line of union, he knows that his material 

 would chip off on the slightest vibration. 



" Now apply this principle to the skull ; the outer table, which re- 

 sembles wood, is indented and dove-tailed ; the inner glassy table has 

 its edges simply laid in contact." Paxton. 



t Muscles are the fleshy parts of the body which surround the bones, 

 having a fibrous texture j a muscle being composed of a number of 



