THE NECK. 



surface of these muscles down behind the sternum in front of the innominate veins 

 and arch of the aorta. 



Pus between the pretracheal and prevertebral layers cannot go further to one 

 side than the sheath of the vessels. Therefore it follows the trachea and oesophagus 

 down into the posterior mediastinum. This space, between these layers, is some- 

 times called the visceral space because it contains the cesophagus, trachea, and 

 thyroid gland. Pus in this space can also perforate into the trachea, pharynx, 

 cesophagus, or even extend laterally and involve the great vessels. 



If the anterior portion of the thyroid gland suppurates, the pus may perforate the 



Prevertebral layer 

 Cricoid cartilage 



Hyoid bone 



Thryoid cartilage 



Superior layer of deep 

 cervical fascia 



Pretracheal layer 

 Cricoid cartilage 



Thryoid gland 

 Space of Burns - 



Left innominate vein 

 Aorta 



Pericardium 

 FIG. 180. The superficial layer, pretracheal layer, and prevertebral layer of the deep cervical fascia. 



thin pretracheal fascia covering it and pass down behind the sternohyoid and sterno- 

 thyroid muscles into the anterior part of the superior mediastinum. 



Pus posterior to the prevertebral fascia, as from caries of the vertebrae, if high 

 up may bulge into the pharynx, forming a retropharyngeal abscess. It may follow 

 the scaleni muscles and brachial plexus down around the axillary artery into the 

 axilla. In the neck it shows itself posterior to the carotid arteries and to the outer 

 edge of the sternomastoid muscles. 



Pus in the sheath of the great vessels, when originating from lymphatic nodes, 

 may first raise the sternomastoid muscle and show itself along its anterior border; 

 it may perforate the lumen of the vessels; it may pass down with the vessels into the 

 superior mediastinum; or it may bulge into the visceral space between the pre- 

 vertebral and pretracheal layers and follow the trachea and cesophagus down into the 

 chest. Should it tend outwardly it may break into the posterior cervical triangle 

 between the prevertebral and superficial layers and show itself above the clavicle. 



