374 ANATOMY. 



this respect, in different parts of the body [as in the tortoise]. We 

 may observe that, upon the whole, when the skeleton contains the whole 

 or a part of the animal, it consists of fewer parts, with the least mo- 

 tion on each other. Of this shell-fish are the strongest instance, and 

 next the lobster, turtle, tortoise, &c. And even in the quadruped, 

 bird, &c, where the bones are in great numbers, having motion on each 

 other, yet we find the skull to accord with the above-stated principle. 

 The cuttle-fish [_Sepia~] might be cited as an exception to this, for it has 

 only one bone for its skeleton, which is not on the outside, and in 

 some kinds \Lol'igo\ the internal skeleton is a horny substance. 



I shall begin my history of the different kinds of skeleton with the 

 most simple in regard to use, which may be as simple in regard to 

 substance and construction. I conceive that where the skeleton has 

 the least rigidity, it is least complicated in its uses ; and this idea is 

 verified in those animals where the skeleton is found to be of most varied 

 use. For in those at the age where this part of the animal can be of 

 little use, the most rigid skeleton does not exist ; but only the soft, or 

 that which I conceive to be of least use : and as the actions of the 

 animal increase, rigidity becomes more and more requisite or useful ; 

 and the soft is changed to the rigid, as will be observed when on the 

 skeleton of each class of animals. The membranous skeleton must have 

 the fewest parts; and we fiud that the most inferior animals have only 

 this kind. 



The membranous skeleton is the first, and appears to be more of a 

 tendinous than membranous nature : it is to be considered rather as a 

 medium for muscular union, so as to give fixed points of action to distinct 

 muscles in the flexible animals of the lowest order ; a worm may be 

 given as an illustration. Every ring in this animal may be considered 

 as a bone, or fixed point, from which muscles pass to the other ring. 

 The same substance is carried to different parts in higher animals, so as 

 to supersede bone, where it can answer the same purpose ; and either 

 where no harder substance is wanted, or would be hurtful ; thus tendons 

 of muscles and ligaments of bone are to be considered as a part of the 

 skeleton ; they certainly make part of the skeleton of the animal*. In 

 the head of the infant, as at a period when the contents are in no danger 

 of being injured, the skeleton is only a membrane, the function being 

 simply that of a containing part : its becoming bone afterwards is to 



* In my history of muscles, in which I treated on tendons, I considered them 

 more as a part of the skeleton than muscles 1 . 



1 [Hunter here refers to his " Crooniau Lectures on Muscular Motion." See my 

 edition of the ' Animal Economy,' 8vo. 1837, p. 229.] 



