228 THE ARTICULATIONS OF THE HORSE 



THE PASTERN JOINT 



This, the proximal interphalangeal articulation (Articulatio interphalangea 

 proximalis s. phalangis secundse), is a ginglymus formed by the junction of the 

 distal end of the first phalanx and the proximal end of the second phalanx. 



The articular surfaces are: (1) On the first phalanx, two slightly unequal con- 

 vex areas Avith an intermediate shallow groove; (2) on the second phalanx, a cor- 

 responding surface, completed behind by a plate of fibro-cartilage. 



TSfcioint capsule is close-fitting in front and on the sides, where it blends with 

 the ex^p^r tendon and the collateral ligaments respectively. Behind it pouches 

 upward^'a Jittle and is reinforced by the straight sesamoidean ligament and the 

 branches of the superficial flexor tendon. 



There are two collateral and four volar ligaments. 



The collateral ligaments, medial and lateral (Lig. coUaterale radiale, ulnare), 

 are very short and strong bands which are attached above on the eminence and de- 

 pression on each side of the distal end of the first phalanx, and below on the em- 

 inence on each side of the proximal end of the second phalanx. The direction of 

 the ligaments is about vertical and, therefore, does not correspond to the digital 

 axis. 



The volar ligaments (Ligg. volaria) consist of a central pair and lateral and 

 medial bands which are attached below to the posterior margin of the proximal end 

 of the second phalanx and its complementary fibro-cartilage. The lateral and 

 medial ligaments are attached above to the middle of the borders of the first phalanx, 

 the central pair lower down and on the margin of the triangular rough area. 



These ligaments are very oommoiily thickened as a result of chronic inflammation, and then 

 are not well defined. The central ones blend below with the branches of the superficial flexor 

 tendon and with the straight sesamoidean ligament. 



Movements. — These are very limited, and consist of flexion and extension. 

 The axis of motion passes transversely through the distal end of the first phalanx. 

 In the standing position the joint is extended. A small amount of volar flexion is 

 possible, and in this position slight lateral and medial flexion and rotation can be 

 produced by manipulation. Dorsal flexion is prevented by the lateral, volar, and 

 straight sesamoidean ligaments. 



THE COFFIN JOINT 



This joint, technically termed the distal interphalangeal articulation (Articu- 

 latio interphalangea distalis s. phalangis tertise), is a ginglymus formed by the junc- 

 tion of the second and third phalanges and the distal sesamoid bone. 



Articular Siurfaces. — The surface on the distal end of the second phalanx is 

 convex in the sagittal direction, concave transversely. The articular surface of the 

 third phalanx slopes sharply upward and forward; its central part is prominent, 

 and is flanlved by two glenoid cavities. It is completed behind by the articular 

 surface of the distal sesamoid or navicular bone. 



Joint Capsule. — This is attached around the margins of the articular surfaces. 

 In front and on the sides it is tight, and is blended with the extensor tendon and the 

 collateral ligaments respectively. It forms a considerable pouch behind, which 

 extends upward to about the middle of the second phalanx, where it is separated by 

 a flbrous membrane from the digital synovial sheath. On each side small pouches 

 project (especially during volar flexion) against the cartilages of the third phalanx 

 just behind the collateral ligaments. ^ 



Ligaments. — The collateral ligaments, medial and lateral (Lig. collaterale 



^ This should be noted ia regard to resection of the cartilage or other operations in this 

 ^dcinity. 



