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, ete. 
Detailed description of the sutures has not sufficient clinical value to justify much addition 
to the statements made in the osteology in this connection. The obliteration or closure 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 vears. 
The symphysis mandibule 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 em.) in length. The chief move- 
ment is hinge-like, the axis of motion passing transversely through both joints. 
The intercornual 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-cornual 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 movements of the hyoid 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; 
