208 CLINICAL APPLIED ANATOMY. 



Chronic nuclear degeneration producing this type of paralysis 

 may exist alone or be a part of tabes, general paralysis, syrin- 

 gomyelia or amyotrophic lateral sclerosis. Acute affections of 

 the nucleus may occur in haemorrhage or softening of the medulla. 

 Since the reflex arc is interrupted, loss of the palatine, pharyngeal 

 and laryngeal reflexes may be expected in nuclear lesions, whereas 

 they are retained in lesions above the level of the nucleus. 



In the membranes at the base of the brain and also at the base 

 of the skull, the glossopharyngeal, vagus and bulbar accessory 

 nerves are close together and are in addition joined by the spinal 

 portion of the accessory nerve. The last nerve is distributed 

 to the sternomastoid and trapezius, consequently the involvement 

 of these two muscles as well as the larynx, palate and pharynx 

 points to a lesion of the membranes or bones of the base. Basal 

 meningitis, basal tumours and aneurysms of the vertebral artery 

 are lesions which may cause this combination of paralyses. 



The action of the laryngeal motor mechanism is easily investi- 

 gated with the laryngoscope and may afford valuable indications 

 not only in disease of the bulbar nuclei but also in certain 

 intrathoracic diseases such as tumour and aneurysm which also 

 cause laryngeal paralysis. 



The superior laryngeal nerve, which conveys motor impulses 

 to the crico-thyroid muscle, is also the sensory nerve of the upper 

 part of the larynx. The nerve trunk is comparatively short and 

 running deeply is well protected, consequently isolated paralysis 

 of the crico-thyroid muscle is exceptional. Suicidal wounds of 

 the neck and tumours or enlarged glands in this position may 

 involve the nerve. The crico-thyroid may also be paralysed by 

 lesions of the vagus at or above the level of the ganglion of the 

 trunk from which the superior laryngeal nerve is given off, but 

 then the other laryngeal muscles will also be affected. The 

 function of the crico-thyroid is to tilt backwards the cricoid 

 cartilage, and so render tense the vocal cords. 



The motor fibres for the other laryngeal muscles run in the 

 recurrent laryngeal nerves. The long course of these nerves 

 exposes them to damage in widely separated localities. Bilateral 



