PEOGEESSIVE MUSCULAR ATROPHY. 219 



segments or both. In paralysis of the lower arm type the 

 flexors and extensors of the wrists and fingers and the small 

 muscles of the hand are involved. Sometimes the intrinsic 

 muscles of the hand suffer alone. The supinator longus usually 

 escapes. The lesion in the cord occupies the seventh and eighth 

 cervical and the first dorsal segments. The deformity known as 

 claw hand may result. 



In paralysis of the upper arm type the scapular muscles, 

 deltoid, triceps and supinator longus are involved. The lesion 

 corresponds to the fifth and sixth cervical segments. The dis- 

 tribution of the paralysis is very similar to that met with as the 

 result of lesions of the fifth and sixth cervical roots in the 

 posterior triangle of the neck. The paralysis of the deltoid 

 allows the humerus to fall away from the glenoid cavity simu- 

 lating dislocation. This deformity is more marked if the supra- 

 spinatus as well as the deltoid is paralysed. 



When the spinal muscles are paralysed, certain curvatures of 

 the spine occur, owing to loss of muscular support and the 

 unopposed action of unparalysed muscles. Spinal curvature may 

 also result from tilting of the pelvis when muscles attached to 

 this are weak. 



The paralysed limbs often show vaso-motor disturbance, 

 stunted growth and thinning of the bones. These changes are 

 due to the involvement of the centres in the cord which supply 

 vaso-motor and trophic fibres and also in part to disuse of the 

 limbs. Pain is sometimes complained of at the onset of the 

 disease, actual anaesthesia is found in rare cases, and persistent 

 hyperalgesia is not uncommon. Diffusion of the lesion in the 

 grey matter of the cord, to the adjacent tracts for painful impulses 

 and for common sensation, probably explains these occurrences. 



PROGRESSIVE MUSCULAR ATROPHY. 



This affection is sometimes called chronic anterior polio- 

 myelitis. 



An anatomical difference lies at the root of the two types of 



