218 THE ARTICULATIONS OF THE HORSE 



various periods during development and growth. Their importance lies in the 

 fact that so long as they persist, continuous growth is possible. They are usually 

 designated according to the bones which enter into their formation, e. g., spheno- 

 squamous, naso-frontal, etc. 



Detailed description of the sutures has not sufRcient clinical value to justify much addition 

 to the statements made in the osteology in this connection. The obliteration or closiu'e of the 

 sutures is, however, worthy of brief mention. The cranial sutures are usually all closed at seven 

 years, but the apex only of the petrous temporal is fused with the occipital and squamous temporal. 

 Most of the facial sutures are practically closed at ten years, although complete synostosis may in 

 some be delayed for years or may not occur at all; the nasal suture, for example, usually persists 

 even in advanced age, so far as its anterior part is concerned. 



The principal synchondroses are: (1) That between the basilar part of the 

 occipital bone and the body of the sphenoid (Synchondrosis spheno-occipitalis) ; 

 (2) that between the presphenoid and postsphenoid (Synchondrosis intersphenoid- 

 alis); (3) those between the parts of the occipital bone (Synchondroses intraoc- 

 cipitales). The first is ossified at four or five years, the second at three years, and 

 the occipital bone is consolidated at two years. 



The sjrmphysis mandibulae ossifies at one to six months. 



THE HYOIDEAN ARTICULATIONS 



The temporo-hyoid articulation is an amphiarthrosis, in which the articular 

 angle of the dorsal end of the great cornu of the hyoid bone is attached by a short 

 bar of cartilage to the hyoid process of the petrous temporal bone. The cartilage 

 (Arthrohyoid) is about half an inch (ca. 1-1.5 cm.) in length. The chief move- 

 ment is hinge-like, the axis of motion passing transversely through both joints. 



The intercomual articulation is an amphiarthrosis formed by the junction of 

 the ventral extremity of the great cornu with the dorsal end of the small cornu of 

 the hyoid bone. They are united by a very short piece of cartilage, in which there 

 is usually a small nodule of bone in the young subject. This nodule, the epihyoid 

 or middle cornu, is usually fused with the great cornu in the adult. The chief 

 movement here is also hinge-like, the angle between the cornua being increased or 

 diminished. 



The basi-comual articulation is a diarthrosis formed by the junction of each 

 small cornu with the body of the hyoid bone. The small cornu has a concave facet 

 which articulates with the convex facet on either end of the dorsal surface of the 

 body. The capsule is ample enough to allow considerable movement, which is 

 chiefly hinge-like. 



The m.ovements of the hj^oid bone are concerned chiefly in the acts of mastica- 

 tion and swallowing. In the latter the ventral parts of the hyoid bone are moved 

 forward and upward, carrying the root of the tongue and the larynx with them, 

 and then return to their former position. 



The Articulations of the Thoracic Limb 



In the absence of the clavicle the thoracic limb forms no articulation with the 

 trunk, to which it is attached by muscles. The movement of the shoulder on the 

 chest-wall is chiefly rotation around a transverse axis passing through the scapula 

 behind the upper part of the spine. 



THE SHOULDER JOINT 



The shoulder .or scapulo-humeral joint (Articulatio scapulo-humeralis) is 

 formed by the junction of the distal end of the scapula with the proximal end of 

 the humerus. The articular surfaces are: (1) On the scapula, the glenoid cavity; 



