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Chapter XIII. 



THE SKELETON OF THE RABBIT. Lepus cuniculus. 



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, 



