132 THE NERVOUS SYSTEM 



the posterior triangle of the neck and runs along the vertebral 

 border of the scapula to supply the rhomboids, major and 

 minor. 



These two muscles arise from the spines of the upper 

 thoracic and lower cervical vertebrae, and pass downwards and 

 laterally to be inserted into the vertebral border of the 

 scapula. When they contract, they draw the scapula upwards 

 and medially, thus helping to brace back the shoulders. 

 In paralysis of the rhomboids, the weight of the upper limb 

 draws the scapula downwards and, as the lower part of the 

 serratus anterior is unopposed, the inferior angle is tilted in a 

 lateral direction. The condition is determined by a careful 

 comparison of the relative positions of the two scapulae. 



4. The Long Thoracic Nerve (of Bell) arises by three roots, 

 which spring from the fifth, sixth and seventh cervical nerves, 

 before the formation of the trunks of the brachial plexus. 

 It enters the axilla and descends on the medial wall to supply 

 the serratus anterior. 



The Serratus Anterior arises from the upper eight ribs, a 

 little in front of the mid-axillary line, and its fibres pass 

 backwards, round the chest wall and closely applied to it, to 

 be inserted into the ventral aspect of the vertebral border of 

 the scapula. When the muscle contracts, it draws the scapula 

 forwards and laterally and, at the same time, it rotates it 

 clockwise (as seen from in front). 



Movements of flexion and abduction at the shoulder-joint 

 itself are limited to 90, and, although these movements can 

 apparently be carried out to an angle of about 160, the 

 additional range is obtained by movements of the shoulder- 

 girdle as a whole. This additional movement is produced 

 mainly by the serratus anterior and the trapezius. 



The serratus anterior plays an important part in forward 

 pushing movements, but it is aided by the trapezius and the 

 rhomboids, which help to steady the scapula. When the 

 long thoracic nerve is injured alone, the patient cannot 

 flex his arm beyond a right angle, and if the arm is passively 



