228 THE ARTICULATIONS OF THE HORSE 
THE PASTERN JOINT 
This, the proximal interphalangeal articulation (Articulatio interphalangea 
proximalis s. phalangis secunde), 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 with an intermediate shallow groove; (2) on the second phalanx, a cor- 
responding surface, completed behind by a plate of fibro-cartilage. 
The joint capsule is close-fitting in front and on the sides, where it blends with 
the extensor tendon and the collateral ligaments respectively. Behind it pouches 
upward a little 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. collaterale 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 commonly 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 tertiz), is a ginglymus formed by the june- | 
tion of the second and third phalanges and the distal sesamoid bone. 
Articular Surfaces.—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 flanked 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 fibrous 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 
1This should be noted in regard to resection of the cartilage or other operations in this 
vicinity. 
