THE BRACHIAL PLEXUS 101 



Cord may be torn or stretched in subcoracoid dislocation of 

 the humerus or by the " heel in axilla " method of reduction. 

 Sensory changes are found in the areas supplied by the ulnar, 

 and the medial cutaneous nerves of the arm and forearm (Fig. 

 12). All the muscles supplied by the medial cord are paralysed, 

 i.e. the intrinsic muscles of the hand, supplied by the ulnar and 

 medial head of the median, and the flexor carpi ulnaris and the 

 ulnar part of the flexor digitorum profundus, both supplied by 

 the ulnar nerve. 



The Lateral Cord may be injured in the same way. All 

 the muscles supplied by the musculo-cutaneous nerve (biceps, 

 coraco-brachialis, and brachialis, partly) and by the lateral head 

 of the median (superficial and deep muscles of front of forearm) 

 (p. 72) are paralysed. Partial epicritic insensibility exists in 

 the areas supplied by the musculo-cutaneous and median nerves 

 (Fig. 12). 



Injury of the Posterior Cord produces all the signs of 

 combined radial (musculo-spiral) and axillary (circumflex) 

 paralyses. 



Lesions of the Infra-clavicular Branches of the 

 Plexus. Axillary (Circumflex) Nerve. When this nerve is 

 paralysed (p. 39) the deltoid atrophies and the bony land- 

 marks become prominent a condition which must be differ- 

 entiated from wasting of the muscle following disease of the 

 shoulder-joint. Lateral rotation is not greatly affected by the 

 paralysis of the teres minor, but abduction can only be produced 

 by the supra-spinatus. A marked loss of epicritic and proto- 

 pathic sensibilities over the distal part of the deltoid always 

 accompanies injury to the axillary (circumflex) nerve. 



The Radial (Musculo-Spiral) Nerve may be pressed on in 

 the axilla, e.g. " crutch " and " Saturday-night " paralysis. 

 It is damaged in 8 per cent of fractures of the distal two- 

 thirds of the shaft of the humerus, either at the time of the 

 accident or in the subsequent formation of callus, and it has 

 occasionally been injured in wiring ununited fractures of the 

 humerus. 



The Dorsal Interosseous Nerve is sometimes injured in 

 fractures of the neck of the radius and in dislocations of that 

 bone. It may be cut in operations which involve incisions 

 into the supinator (s. brevis) (p. 65). The Superficial Branch 

 of the Radial Nerve (Radial Branch of Musculo-Spiral) may be 

 injured in wounds about the lateral and dorsal aspects of the 



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