336 CLINICAL APPLIED ANATOMY. 



sheaths of the great branches of the aorta, the neoplasm may find 

 its way to the root of the neck and into the posterior triangles. 



Carcinomata are said to be more destructive in their growth, 

 infiltrating, and so destroying, rather than surrounding, the 

 vessels and nerves with which they come in contact. 



Any of the nerves in the thorax may be involved in mediastinal 

 growths. The recurrent laryngeal nerves have already been 

 mentioned. The fact that the phrenic nerves and the vagi 

 completely traverse the chest affords many chances for their 

 compression. Implication of one phrenic nerve will produce 

 unilateral paralysis of the diaphragm. Disturbance of the 

 branches of the vagus probably accounts for the asthmatic 

 paroxysms of dyspnoea which sometimes accompany mediastinal 

 tumours, the vagus being the motor nerve to the bronchial 

 muscles. A growth in the superior mediastinum may involve 

 the brachial plexus, or pressing on the orbital fibres of the 

 sympathetic produce ptosis and myosis, but these occurrences 

 are rare. In both superior and posterior mediastina the inter- 

 costal nerves and even the spinal column may be attacked. 

 The intervertebral foramina allow the growth, by tracking along 

 the vessels and nerves, to reach the interior of the spinal canal. 



Venous obstruction is a common and striking phenomenon 

 of mediastinal growth, but may also occur in connection with 

 aneurysm and mediastinitis. The veins most likely to suffer are 

 the superior vena cava and the two innominates. The azygos 

 veins are sometimes occluded. The inferior vena cava rarely 

 suffers ; its extremely short course in the thorax and its remote- 

 ness from the principal groups of glands no doubt account for its 

 comparative immunity. Obstruction of the superior vena cava 

 produces congestion in the areas of its tributaries. The parts 

 involved are the head, face, tongue, fauces, ears, neck, arms, and 

 chest. The circulation within the cranium is obstructed, the 

 nasal mucous membrane is turgid and inclined to bleed ; even 

 exophthalmos and conjunctival haemorrhage may result. If only 

 one innominate or one subclavian vein be obstructed the area of 

 congestion is more restricted. In some instances of compression 



