LAKYNGEAL PAEALYSIS. 209 



paralysis may be produced by cancer of the upper parts of the 

 oesophagus or by tumours of the thyroid gland or operations at 

 the root of the neck on either of these structures, for both 

 recurrent nerves are in close contact with the sides of the gullet 

 and the thyroid. The left recurrent nerve, winding as it does 

 round the aortic arch, is frequently compressed by aortic 

 aneurysms, whilst aneurysms of the innominate or right sub- 

 clavian arteries may paralyse the right nerve, but this is more 

 commonly implicated in glandular enlargements within the 

 thorax and may be damaged by phthisis near the pleural dome. 



In progressive lesions of the recurrent laryngeal nerve the 

 muscles usually fail in a definite order according to Semon's law, 

 the abductors first and then the adductors. The nerve bundles 

 in the recurrent laryngeal trunks for the abductor and the 

 adductor groups are distinct, but this anatomical arrangement 

 does not altogether explain the greater vulnerability of the 

 abductors. They have been compared in this respect to the 

 extensor muscles of the limbs. 



In abductor paralysis the paralysed cord during inspiration 

 appears both shorter and higher than its fellow. This appearance 

 is due to the sloping surface of the cricoid facet on which the 

 arytenoid cartilage rests, so that when the abductors come into 

 play the latter cartilage is dragged downwards as well as back- 

 wards and outwards. The free edges of the true cords are 

 directed upwards as well as inwards, and when the abductors 

 of both sides are paralysed the inspiratory rush of air tends 

 to drive the cords together like a valve, producing urgent 

 dyspnoea. 



The arytenoideus muscle escapes in unilateral laryngeal 

 paralysis, possibly because it is supplied by both recurrent nerves. 



Paralysis of the soft palate also points to an affection of the 

 motor fibres of the vago-glossopharyngeal group. The lowermost 

 fibres are those concerned, and these are usually spoken of as the 

 bulbar accessory fibres. They arise from the nucleus ambiguus 

 and supply the levator palati, probably reaching the palate 

 through the pharyngeal plexus. Hence the palate is paralysed 



C.A.A. 14 



