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i ae 
THE UPPER EXTREMITY. ses 
articulation with the sternum forms essentially a weak joint which is liable to be 
dislocated, especially from blows upon the outer part of the shoulder which drive 
the inner end of the clavicle forwards against the weak anterior sterno-clavicular 
ligament. The shaft of the ciavicle, subcutaneous throughout, is weakest at the 
junction of its two curves; it is in this region that the bone is so frequently 
fractured as the result of force transmitted through it to the trunk. The dis- 
placement of the outer fragment varies according to whether the break takes place 
internal or external to the coraco-clavicular ligament ; in the former case the weight 
of the upper extremity, acting through the coraco- clavicular ligament, pulls the 
outer fragment downwards ; when the fracture is external to the ligament, the outer 
end of the clavicle rotates forwards, but there is no downward displacement. The 
outer end of the clavicle is on a plane posterior to its inner end, so that the shoulder is 
braced backwards away from the thorax; hence in fractures of the clavicle, both 
inside and outside the coraco-clavicular ligament, the point of the shoulder rotates 
forwards and inwards. The acromio-clavicular articulation is somewhat difficult to 
feel; the groove which corresponds to it runs in the sagittal direction, and hes 
14 ie internal to the outer border of the acromion, and immediately external to a 
slight prominence upon the outer extremity of the clavicle. W hen this joint is 
dislocated the clavicle almost imvariably ov errides the acromuon, and the summit 
of the shoulder presents a somewhat conical or “sugar-loat” appearance. 
The tip of the acromion looks directly forwards, and les a finger’s breadth 
external to and a little in front of the outer extremity of the clav icle. The outer 
border of the acromion can readily be followed to its Junction with the spine of the 
scapula, and the latter to its root, which is situated on a level with the third dorsal 
spine. The inner border of the acromion and the posterior border of the outer end 
of the clavicle meet at an angle into which the point of the finger can be pressed. 
The upper angle of the scapula, covered by the trapezius and the supraspinatus 
muscles, is too deeply placed to be palpated distinctly. The inferior angle, and 
the internal border, from the root of the spine downwards, form visible prominences 
which are readily felt; the former overlies the seventh intercostal space on a level 
with the seventh dorsal spine, while the latter les a ttle internal to the angles of 
the ribs. 
To elicit crepitus in a transverse fracture of the scapula below the spine, the surgeon 
stands behind the patient and grasps the upper fragment by placing the forefinger upon 
the coracoid and the thumb upon the spine, while with the other hand he grasps the 
inferior angle ; the two fragments are then moved the one upon the other. 
The tip of the coracoid process may be felt by pressing the finger firmly upon the 
anterior border of the deltoid at a poimt 1 in. below the junction of the middle 
and outer thirds of the clavicle. Internal to the coracoid is a triangular depres- 
sion which corresponds to the upper end of the interval between the clavicular 
fibres of the pectoralis major and deltoid muscles. Behind this triangular depres- 
sion are the termination of the cephalic vein, a lymphatic gland, the first part of 
the axillary vessels, and the cords of the brachial plexus. By firm pressure in this 
situation the pulsation of the axillary artery can be felt, and by further pressure 
the circulation in the vessel can be arrested by compressing the artery against the 
second rib. The first part of the axillary artery may be cut down upon either by 
a transverse incision through the clavicular origin of the pectoralis major, or by a 
longitudinal incision in the interval between this muscular shp and the deltoid. 
The companion vein lies in front of, as well as to the thoracic side of the artery, 
thus adding to the difficulty of exposing the vessel. In fractures of the middle 
third of the clavicle the subclavian vessels are protected by the soft pad formed by 
the subclavius muscle. 
The upper end of the humerus covered by the deltoid gives rotundity to the 
shoulder. The greater tuberosity projects beyond the acromion, and constitutes the 
most external bony landmark of the shoulder. When the head of the bone is dis- 
located, the outer border of the acromion then becomes the most external bony 
landmark, and the shoulder presents a square contour. The lesser tuberosity, small 
but conical, can be felt through the deltoid. Pointing directly forwards, it les 
