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ACROMIO-CLAVICULAR JOINT. 267 
the conoid ligament. Superiorly it is attached to the trapezoid ridge on the under 
surface of the acromial end of the clavicle. Its outer and inner borders are free. 
Its anterior surface is principally directed upwards, and its posterior surface, to a 
similar extent, looks downwards. 
A synovial bursa usually occupies the re-entrant angle between these two 
ligaments. 
Movements at the Clavicular Joints —The movements of the inner end of the clavicle at 
the sterno-clavicular joint are limited in their range, owing to the tension of the ligaments. 
When the shoulder is raised or depressed the outer end of the clavicle moves upwards and 
downwards, whilst its sternal end glides upon the surface of the interarticular meniscus within 
the joint ; when, on the other hand, the shoulder is carried forwards or backwards, the inner end 
of the clavicle, along with the interarticular meniscus moves upon the sternal facet. In 
addition to these movements of elevation, depression, forward movement and backward movye- 
ment of the clavicle, there is also allowed at the sterno-clavicular joint a certain amount of 
circumduction of the clavicle. 
The part which is played by certain of the ligaments in restraining movement requires 
eareful consideration. The rhomboid ligament checks excessive elevation of the shoulder, and 
restrains within certain limits both backward and forward movement of the clavicle. When the 
clavicle is depressed, as in cases where a heavy weight, such as a bucket of water, is carried in the 
hand, it receives support by resting upon the first rib, and the tendency for the inner end of the 
bone to start up out of its sternal socket is obviated by the tension of the interarticular 
meniscus, the interclavicular ligament, and the anterior and posterior sterno-clavicular 
ligaments. 
The interarticular meniscus not only acts as a cushion which lessens the shock of blows 
received upon the shoulder, but it also acts as a most important bond of union, and prevents the 
inner end of the clavicle from being driven upwards upon the top of the sternum when force is 
applied to its outer end. 
The movements at the acromio-clavicular joint are of such a kind as to allow the inferior 
angle, and to some extent the base of the scapula, to remain more or less closely applied to the 
chest-wall during the various movements of the shoulder. The strong connexion between the 
coracoid process and the acromial end of the clavicle, by means of the conoid and trapezoid 
ligaments, renders it necessary that the scapula should follow the clavicle in its various 
excursions. The presence of the acromio-clavicular joint, however, enables the scapula to change 
its position somewhat with reference to the clavicle as the shoulder is moved. Thus, when the 
shoulder is raised and depressed, a marked difference takes place in the angle between the two 
bones; again, when the shoulder is thrown forwards or backwards, these movements can be 
performed without altering in a material degree the direction of the glenoid cavity of the scapula, 
or in other words, the socket of the shoulder-joint. 
The conoid and trapezoid ligaments set a limit upon the movements of the scapula at the 
acromio-clavicular joint. They both, but more particularly the trapezoid ligament, prevent the 
acromion process of the scapula from being carried inward below the outer end of the clavicle 
when blows fall upon the outer aspect of the shoulder. 
LIGAMENTS OF THE SCAPULA. 
These ligaments are not directly connected with any articulation. The coraco- 
acromial ligament (lig. coraco-acromiale, Fig. 209) completes the arch between the 
coracoid and acromion processes of the scapula, and thus provides a secondary 
socket for the greater protection and security of the shoulder-joint. It is a flat 
triangular structure stretched tightly between its lines of attachment. By its base 
it is fixed to a varying amount of the postero-external border of the coracoid 
process, and by its narrower apical end to the tip of the acromion process, im- 
mediately external to the acromio-clavicular joint. Its surfaces look upwards and 
downwards, and its free borders outwards and inwards. It is thinnest in the 
centre, where it is sometimes perforated by a prolongation of the tendon of the 
pectoralis minor. ; 
The suprascapular ligament (lig. transversum scapulee superius) is a distinct but 
short flat band which bridges the notch of the same name. It may be continuous 
with the conoid ligament, and it is frequently ossified. As a rule the foramen 
completed by this hgament transmits the suprascapular nerve, while the corre- 
sponding vessels travel above the ligament to reach the supraspinous fossa. 
A small duplicate of this ligament may often be found bridging the foramen on 
its ventral aspect, subjacent to which small branches of the suprascapular artery 
return from the supraspinous to the subscapular fossa. 
The spino-glenoid ligament (lig. transversum scapule inferius) consists of 
another set of bridging fibres which are situated on the posterior aspect of the 
