THE FETLOCK JOINT 



185 



THE FETLOCK JOINT 

 This, the metacarpo-phalangeal articulation (Articulatio metacarpo-phalangea), 

 is a ginglymus formed by the junction of the distal end of the large (third) meta- 

 carpal bone, the proximal end of the first phalanx, and the proximal sesamoid 

 bones. 



Articular Surfaces. — The surface on the large metacarpal Iwne is approxi- 

 mately cylindrical in curvature, but is divided into two slightly unequal parts by a 

 sagittal ridge. This is received into a sort of socket formed l^y the first phalanx 



below and the two sesamoids together 

 with the intersesamoid ligament be- 

 hind. The latter is a mass of fibro- 

 cartilage in which the sesamoid bones 

 are largely embedded. It extends 

 above the level of the sesamoids, 

 and is grooved to receive the ridge 

 on the metacarpal bone; its posterior 

 surface forms a smooth groove for the 

 deep flexor tendon. 



The joint capsule is attached around 

 the margin of th(^ articular surfaces. It 



Branches of 

 suspensory ligament 



Fig. 148. — Sagittal Section op Distal Part of Limb 

 OF Horse. 

 1, Large metacarpal bone; 3, fetlock joint; 4, 

 proximal se.samoid bone; 5, first phalanx; 6, pastern 

 joint; 7, second phalanx; 8, coffin joint; 9, third phal- 

 anx; W, distal sesamoid (navicular bone); 13, suspen- 

 sory ligament; 14. deep flexor tendon; 15, superficial 

 flexor tendon; 16, posterior annular ligament of fetlock; 

 30, inferior sesamoidean ligaments; ;?/, extensor tendon; 

 .?4> plantar cushion; i'J, periople; 25. wall of hoof; 29, 

 sole of hoof; .1, navicular bursa, proximal part. (After 

 Ellenberger-Baum, Anat. fiir Kiinstler.) 



Fig. 149. — Articular Surfaces of First Phalanx 

 .\ND Sesamoids at Fetlock, with Intersesa- 

 moid AND Suspensory Ligaments. (After 

 Schmaltz, Atlas d. Anat. d. Pferdes.) 



is thick and ample in front; here a 

 bursa is interposed between it and 

 the extensor tendons, but the tendons 

 are also attached to the capsule. Pos- 

 teriorly it forms a thin-walled pouch 

 which extends upward between the 

 metacarpal ]:)one and the suspensory ligament about as high as the point of 

 bifurcation of the latter. The capsule is reinforced by two lateral ligaments. 



The lateral ligaments, external and internal (Ligamentum collaterale ulnare, 

 radiale) are partially divided into two layers: the superficial layer arises from the 

 eminence on the side of the distal end of the large metacarpal bone, and passes 

 straight to the rough lateral area below the margin of the articular surface of the 

 first phalanx; the deep layer, shorter and much stronger, arises in the lateral 

 depression on the distal end of the metacarpal bone, and passes obliquely downward 

 and backward to be inserted into the outer surface of the sesamoid and the proxi- 

 mal end of the first phalanx. 



