SHOULDER JOINT. 365 
a 
very superficial, and incapable of maintaining the former in its place 
without some collateral aid. It is somewhat remarkable that the liga- 
ments of this jot are extremely weak, being confined to the lax fibres 
surrounding the synovial capsule, which is so loose 
that after removing all the other soft parts, and 
making a small opening into the joint, the two bones 
may be readily separated for some distance ; these 
fibres are superiorly fixed around the margin of the 
glenoid cavity, and inferiorly round the head of the 
humerus. Chauveau states that a igament descends 
from the coracoid process of the scapula, which 
diverges and becomes inserted into the tubercles at 
the anterior part of the head of the humerus. He also 
states that it is loose, and therefore facilitates much 
motion, but it is not easy to separate it from the 
capsular ligament. This is longer posteriorly than 
anteriorly, and presents postero-laterally two stays, 
similar to two pieces of tape. The external one, 
arising from the outer lip of the glenoid cavity, is 
attached to the outer and back part of the head of 
the humerus. The internal one arises from the 
inner edge of the glenoid cavity, and is attached to 
the inner and back part of the head of the humerus. 
Dut this deficiency in ligaments is made up by a 
much more powerful material in resisting disloca- 
tions. The whole joint is surrounded by elastic Fic 9. 
muscular fibre or by tendinous bands, having the PROFIE VIEW oF Tus 
: 5 2 SCAPULO-HUMERAL, OR 
same kind of support—thus it has in close appo- — Sxovrprr Joryr. 
sition the following muscles, viz.— oS eae eee 
7 3 B. Coracoid process of 
Anteriorly, the Coraco Humeralis, and Flexor scapula. 
Brachii. Vai eae 
Externally, the Antea Spinatus, and Postea Spi- D. Rimof glenoid cavity. 
natus E. Superior third of hu- 
2 merus. 
. Posteriorly, the Scapulo-Humeralis Posticus, &c. 3. Capsular ligament. 
‘ Z a 2. Tendon of the coraco- 
Internally, the Subscapularis, &e. radialis muscle. 
Whenever, therefore, any violent strain is thrown upon the joint, which 
would force the head of the humerus forwards, the Coraco Humeralis and 
Flexor Brachii contract and prevent the accident. In the same manner, 
each of the above muscles acts in its own direction, and the result is that 
dislocation of the humerus in the horse is extremely rare. 
THE MOVEMENTS OF THE SHOULDER JOINT in the horse are much more 
Nmited than in man, and indeed they are almost confined to flexion and 
extension. When all the muscles are cut away from the joint, rotation 
and circumduction may be easily effected ; but in examining its movements 
during life, it will be evident that neither one nor the other of these acts 
can be effected in any appreciable degree ; this is at once proved if it is 
attempted to turn the foot inwards or outwards, when it is flexed at the 
knee, during the life of the horse, for beyond the slight motion of the 
whole limb, including the scapula, the foot is firmly fixed, and there is 
not the slightest rotation or circumduction at the shoulder joint, With- 
out the power of pronation and supination possessed by man, and partially 
by the dog and cat, the above actions would be worse than useless, and it 
is altogether a mistake to ascribe to any other of the domestic animals, aa 
