ARTICULATIONS OF THE ANTERIOR LIMBS. 203 



of the carpus in nearly the same proportions, and both act in an identical manner. 

 Their mechanism is most simple. 



In flexion, the first tier of bones rolls backwards on the radius, the inferior 

 row moves in the same sense on the upper, the metacarpus is carried backwards 

 and upwards, the common posterior ligament is relaxed, the capsular ligament 

 becomes tense, and the articular surfaces, particularly those of the second joint, 

 separate from each other in front. In extensmi, the metacarpus is carried down- 

 wards and forwards by an inverse mechanism. This movement stops when the 

 ray of the forearm and that of the metacarpus are in the same vertical line. In 

 flexioTi, these bones never directly approach each other, the inferior extremity of 

 the metacarpus being always carried outwards. It may also be remarked, that 

 the slight movements of ahdudinn, adduction, and circumduction of the caipus are 

 only possible at the moment when the foot is flexed on the forearm. 



With regard to the plaiiiform diarthroses articulating the carpal bones of the 

 same row, they only allow a simple gliding between the surfaces in contact ; and 

 with the carpo-metacarpal arthrodia it is absolutely the same. The restricted 

 mobility of these various articulations has but a very secondary influence on the 

 general movements of the carpus ; but it nevertheless favours them by permitting 

 the carpal bones to change their reciprocal relations, and adapt themselves, during 

 the play of the radio-carpal and intercarpal hinges, to a more exact coaptation of 

 the articular planes which they form. 



In the other animals, the carpal articulations have the same essential characteristics we 

 have noticed in Solipeds. The four principal peripheral bands differ but little in them; 

 tliough in the Dog and Cat they are lax enough to allow somewhat extensive lateral 

 movements. 



5. Intermetacarpal Articulations. 



Each lateral metacarpal bone articulates with the middle one, by means of 

 diarthrodial and synarthrodial surfaces, for the description of which refer to page 

 112. An interosseous ligament, composed of very short and strong fasciculi, is 

 interposed between the synarthrodial surfaces, and binds them firmly together. 

 Its ossification is not rare. The diarthrodial facets are maintained in contact by 

 the preceding ligament, and by the carpal ligaments inserted into the head of the 

 lateral metacarpal bones. The intermetacarpal articulations only allow a very 

 obscure, vertical, gliding movement. 



In the Ox, there is only one intermetacarpal articulation, which is much simpler than 

 those in the Horse. 



In the Pig, the four metacarpal bones correspond, at their upper extremity, by means of 

 small diarthrodial facets on their sides. Fibrous fasciculi, derived from the great anterior and 

 posterior ligaments of the carpus, protect those intermetacarpal articulations before and 

 behind. Otlier fibres, situated between the adjacent faces of the metacarpal bones, are real 

 interosseous ligaments. 



In the Dog and Cat, the four great metacarpal bones articulate with each other in 

 almost the same manner as in the Pig, but their mobility is greater 



6. Metacarpo-phalangeal Articulation (Figs. 131, 132). 



Preparation. — In order to study the whole of this articulation, it is well to have an anterior 

 limb from the lower fourth of the forearm. From this the tendons of the flexors and extensors 

 of the phalanjres are to be removed, and then the suspensory ligament of ti)e ft-tlock, anterior 

 capsular ligament, lateral ligaments, and the supeificial inferior sesamoid ligiiraeut, can be 

 dissected. To study the ligaments which bind the bnnes forming the inferior articular 

 surface, the first phalanx and sesamoid bones should be removed, which allows of the dissection 



