98 THE SUPERIOR EXTREMITY 



plication, paralysis of the serratus anterior (s. magnus) is 

 frequently accompanied by paralysis of the lower part of the 

 trapezius and by pain, which radiates over the distribution of 

 C. 3 and C. 4. When the serratus anterior is paralysed alone, 

 the patient is unable to flex the humerus above the level of 

 the shoulder. If his arm is passively flexed above that level, 

 forward pushing movements cannot be performed, and attempts 

 to produce them cause marked winging of the scapula. All the 

 other movements, including forward pushing below the shoulder, 

 are intact, and, although the latter is weaker, it does not produce 

 winging of the scapula (Sherren). When in addition the lower 

 fibres of the trapezius (C. 3 and 4) are affected, no forward 

 pushing movement can be performed, and marked winging of 

 the scapula results on its being attempted. 



The Supra-scapular Nerve (p. 127) arises from the upper 

 trunk of the plexus (C. 5 and 6) and supplies the supra- and 

 the infra-spinatus. When it is injured alone a rare occurrence 

 the resulting disability is slight, as lateral rotation of the humerus, 

 though definitely weakened, can still be performed by the 

 teres minor and the posterior fibres of the deltoid. In Erb- 

 Duchenne paralysis (p. 99) the lesion usually occurs proximal 

 to the origin of the supra-scapular nerve, which is therefore 

 involved. 



Lesions of the Brachial Plexus. As the brachial 

 plexus passes towards the axilla its constituent parts converge 

 on one another at the outer border of the first rib, the upper 

 having a downward and the lower an upward inclination. On 

 this account violence applied to the shoulder in a downward 

 direction will cause a stretching or tearing of the upper trunk 

 (Erb-Duchenne type, p. 99), and violence applied in the opposite 

 direction will affect the lower trunk in a similar manner (Klumpke 

 type, p. 100). 



Supra-clavicular lesions of the plexus are generally brought 

 about as the result of trauma (e.g. in complicated labour, in 

 artificial respiration, when a person falling from a height grasps 

 something to save himself, or when the arm of an unconscious 

 patient hangs unsupported over the edge of an operating table), 

 but they may also occur from the pressure of a cervical rib. 



Haemorrhagic extravasation or effusion into a nerve trunk is 

 quite sufficient to produce a temporary paralysis of the muscles 

 supplied. Rapid and complete recovery differentiates this 

 condition from an actual rupture of nerve fibres. 



