THE ANATOMY OF THE HORSE. 45 



musculo-spiral groove ; while inferiorly it passes to be inserted into the 

 external tuberosity at the upper end of the radius. 



The Internal Lateral Ligament forms a longer but more slender 

 cord than the preceding, and passes from a small eminence on the 

 outer side of the lower extremity of the humerus to be inserted into the 

 shaft of the radius below the bicipital tuberosity. Some of the anterior 

 fibres join the tendon of the bicejjs or the anterior ligament, while some 

 of the posterior join the arciform fibres connecting the radius and ulna. 



The Anterior Ligament is of a membranous form. Its upper border 

 is fixed to the humerus, its lower border to the radius, while its lateral 

 borders blend with the lateral ligaments. 



Directions. — The anterior and lateral ligaments should now be cut 

 transversely about their middle in order to expose the interior of the joint. 



The Synovial Membrane will be seen to line the inner face of the 

 anterior and lateral ligaments, but at the back part of the joint there 

 is no ligament and the membrane is suppoi-ted by the muscles. If the 

 finger be passed backwards and upwards, it will enter a process of the 

 synovial capsule which extends upwards into the olecranon fossa, Avhere 

 a pad of fat intervenes between it and the anconeus muscle. Just 

 behind the external lateral ligament the membrane lines the origin of 

 the flexor metacarpi externus. On the inner side of the joint, behind 

 the internal lateral ligament, the membrane lines the tendons of origin 

 of the middle and internal flexors of the metacarpus, and of the super- 

 ficial and deep flexors of the digit. This disposition of the synovial 

 capsule will be rendered more evident by cutting the above-mentioned 

 muscles a few inches below the joint, and then turning their tendons of 

 origin upwards. 



Directions. — The humerus being now completely severed from the 

 radius and ulna, the mode of union of these latter bones should be 

 examined. 



The Radio-ulnar Articulation. — In the adult animal the bones of 

 the fore-arm are fused together below the radio-ulnar arch, by ossification 

 of the interosseous fibres which in the young animal are interposed 

 between the two bones. Above the arch, however, the fibres interposed 

 between the bones do not ossify except in a very old animal, but persist 

 as an interosseous ligament. The union of the two bones is further 

 maintained by arciform fibres passing on each side from the one bone to 

 the other, and blending with the lateral ligaments of the elbow. At the 

 upper part of their opposed surfaces, the two bones respond to each 

 other by two small synovial facets, which, however, have no special 

 synovial membrane, but are lubricated by processes from the synovial 

 capsule of the elbows-joint. 



Movements. — These are inappreciable, the limb of the horse being 

 fixed in a condition of pronation. 



