154 COMPARATIVE ARTHROLOGY. 



together with the annular ligament, form a kind of ring in which the head of 

 the radius slightly revolves, as there is a certain amount of motion between it 

 and the ulna. The radio-ulnar articulation consists of a superior and an 

 inferior rotatory diarthrosis, and an interosseous ligament ; the rotatory 

 movements between these bones are termed pronation and supination, the 

 prone being the normal position of the extremity. The metacarpus is formed 

 similarly to that of the hog, but it is more mobile, and the rest of the articula- 

 tions of the limb resemble those of that animal, with the exception of the 

 distal interphalangeal, where we find anteriorly an elastic ligament which acts 

 as the retractor of the claw, and is stronger and much more active in the cat 

 than in the dog, the claw of the former being much more retractile. Posteri- 

 orly a piece of fibro-cartilage is the analogue of the naviciilar bone, which is 

 wanting. 



The patella has one straight ligament, and the menisci are united. In the 

 tibio-fibular articulation, there is superiorly a diarthrosis, otherwise it is formed 

 on the same plan as that of the hog, as is the tarsal joint, excepting that the 

 astralagus has an inferior head instead of a trochlea. 



