MUSCULAR DYSTROPHY. 137 



In addition the interossei and lumbricales, by means of their 

 attachments to the long extensor of the fingers as that passes 

 over the proximal phalanges, flex those phalanges and extend the 

 two distal ones. The long extensor of the fingers is practically 

 responsible only for the extension of the proximal phalanges to 

 which, paradoxically enough, it is not attached. 



When the interossei and lumbricales are paralysed, the action 

 of the long extensor on the first phalanges, and of the long flexor 

 on the two terminal phalanges of each finger are not antagonised 

 and a claw hand results. The intrinsic muscles of the hand are 

 but rarely involved in the muscular dystrophies. 



The trapezius. The clavicular and the lower portions of 

 this muscle must be considered separately. 



The clavicular portion. When the arm is to be abducted 

 laterally from the body the scapula must lie applied to the back 

 of the thorax in such a way that it can become tilted in a trans- 

 verse vertical plane. This allows the glenoid cavity to be directed 

 upwards and outwards. To permit the scapula to glide backwards 

 into the appropriate position, the outer end of the clavicle is 

 carried directly backwards. This is the function of the clavicular 

 fibres of the trapezius. The deltoid then abducts the arm and 

 the serratus magnus, by tilting the scapula, acromion upwards, 

 completes the elevation. 



The lower portion. This part keeps the scapula in apposition 

 with the thorax during the first part of the action of advancing 

 the arm. When the humerus has been moved by the deltoid 

 through 45 degrees the serratus magnus comes into action and 

 performs a similar function to that of the trapezius, at the same 

 time tilting the scapula. Consequently a slight starting of the 

 vertebral edge of the scapula away from the thoracic wall, or 

 "winging," at the commencement of the advance of the arm 

 may be caused by paralysis of the lower part of the trapezius. 

 If the serratus magnus be intact the deformity will disappear 

 when the arm reaches the horizontal plane, whereas the deformity 

 due to serratus paralysis is at its maximum in this position, 

 especially if a pushing effort be made at the same time. A 



