PEOGEESSIVE MUSCULAE ATEOPHY. 221 



in the same direction as the corresponding surfaces of the 

 fingers. 



Atrophy of the first dorsal interosseus muscle or abductor 

 indicis usually follows that of the thenar muscles. This muscle 

 forms the prominence which is seen on the dorsum of the hand 

 between the metacarpals of the thumb and index finger, and so 

 wasting is easily recognised, at the same time power of abducting 

 the index finger from the mid line of the hand is lost. The 

 appearance of hollows between the other metacarpal bones 

 indicates wasting of the rest of the interossei, whilst wasting of 

 the lumbricales which lie between the tendons of the long flexors 

 in the palm, causes those tendons to become very prominent. 



Besides abducting and adducting the extended fingers the 

 interossei have the task of flexing the first phalanges and 

 extending the other two. Consequently, should they be paralysed 

 some time before the long flexors and extensors of the wrist 

 have followed suit, the claw hand is produced ; this position is 

 the outcome of the loss of action of the interossei, the first 

 phalanges being over-extended, and the other two flexed. 



Still following the order of arrangement of motor cells, the 

 disease involves the flexors of the fingers and wrists before the 

 extensors of the same parts. 



Of the upper arm muscles the deltoid usually suffers first, 

 often with the supra- and infra-spinati, and the clavicular portion 

 of the pectoralis major. 



Muscles which usually escape are the upper part of the 

 trapezius, the sterno-mastoid, and the triceps. The latissimus 

 dor si and lower half of the pectoralis major are late in showing 

 wasting. The last two muscles are innervated from the sixth 

 and seventh cervical segments ; the trapezius by the spinal 

 accessory, which is derived from the second to the sixth cervical 

 segments. The levator anguli scapulae is innervated from the 

 third and fourth cervical segments. 



When the legs waste, the glutei, extensors of the knee, and 

 muscle groups of the front and outer sides of the leg usually 

 suffer. These groups are represented in the lumbar enlargement. 



