94 THE MECHANICAL lUNCTIONS. 



considerable force in recovering its natural length, 

 after it has been stretched. This ligament is par- 

 ticularly strong in the Camel, whose neck is of 

 great length. Many birds are provided with strong 

 elastic ligaments connecting the vertebr?e of the 

 neck with those of the back ; ligaments of the same 

 kind are also employed for retaining the wings 

 close to the body where they are not used in flying: 

 and a similar provision is made in the wings of 

 Bats. The weight of the bulky organs of digestion 

 in herbivorous quadrupeds require some permanent 

 support of this kind ; and this is furnished by a 

 broad, elastic, fibrous band, extended across the 

 lower part of the abdomen. It is particularly strong 

 in the Elephant, which remains more constantly in 

 the horizontal position than most quadrupeds : and 

 it has been remarked that the general cellular tex- 

 ture in this animal has an unusual degree of elas- 

 ticity.* 



Another example of an elastic ligament occurs in 

 that which connects the two shells of bivalve mol- 

 lusca (as those of the oyster and muscle), and which 

 keeps them open when the animal exerts no force 

 to close them. The claws of the Lion, and other 

 animals of the cat tribe, are retracted within their 

 sheaths by means of two strong elastic ligaments. 

 Structures of this kind are employed very exten- 

 sively in the fabric of insects. t 



The animal substance which comes next in the 

 order of density is Cartilage. The purposes for 

 which this kind of structure is employed are those 



* Hunter on the Blood, &c. p. 112. 



t Chabrier, Memoires du Musee, torn. vi. p. 416. 



