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Chaptiee XII. 

 THE SKELETON OP THE RABBIT. 



Lepus cuniciilus. 



In the early stages of development the skeleton of the rabbit 

 consists entirely of cartilage. This primary cartilaginous 

 skeleton agrees in general plan with the skeleton of the dog- 

 fish. 



The skeleton of the adult rabbit is made up of bone, 

 together with a small amount of cartilage. The bones are 

 of two chief kinds. 



(1) Cartilage-bones are so called from their arising in 

 direct relation with the pre-existing cartilage. They make up 

 the greater part of the adult skeleton. 



(2) Membrane-bones are developed independently of the 

 primary cartilaginous skeleton, and are almost confined to 

 the head. They are to be regarded as dermal bones which 

 have lost their connection with the skin, and become in 

 many cases firmly united with the underlying cartilage and 

 cartilage-bones : they are morphologically equivalent to the 

 bony plates forming the bases of the scales in the dog-fish. 



The sesamoid bones form a third class. These are small 

 nodules of bones developed within the tendons of certain of 

 the limb-muscles close to the joints : they modify the action 

 of these muscles by altering the direction in which they 

 pull. 



The teeth of the rabbit are cutaneous structures, com- 

 parable to the scales or teeth of the dog-fish; they are, 



