70 SURGICAL ANATOMY OF THE NECK. 



carotid vessels (vide Pharynx). Passing from the under 

 surface of the sterno-mastoid towards the middle line, 

 it is attached to the hyoid bone, forming an aponeurotic 

 loop on its upper surface, through which runs the tendon 

 of the digastric ; and extending downwards it forms the 

 sheaths of the sterno-hyoid and sterno-thyroid muscles. 

 The lamina forming the posterior portion of the sheath 

 of the sterno-mastoid is attached above to the angle of 

 the jaw and to the base of the styloid process behind, 

 and to the inner side of the parotid gland, forming a 

 septum between it and the submaxillary gland, the stylo- 

 maxillary ligament. The lower portion of this lamina 

 forms the sheath of the carotid vessels, which sheath is 

 divided by septa inclosing internally the carotid artery, 

 externally the internal jugular vein, and posteriorly the 

 vagus nerve; traced downwards and outwards it is found 

 to inclose the omo-hyoid muscle, binding it down to the 

 clavicle, and inclosing the subclavius muscle, passes 

 beneath it into the axilla, to be continuous with its 

 fasciae (vide Axilla). At the root of the neck this fascia 

 is easily demonstrated to be continuous with the peri- 

 cardium. 



That portion of the fascia which is attached to the 

 hyoid bone above, and to the clavicle and sternum be- 

 low, has been supposed to have some influence on respi- 

 ration, inclosing in its reflexions the depressors of the 

 hyoid bone, and sending processes around the great 

 venous trunks. The omo-hyoidei in particular by their 

 contraction tighten it, and being made tense, the calibre 

 of the veins is increased, and as these muscles only con- 

 tract during inspiration, the dilatation of the veins coin- 

 cides with the dilatation of the thorax, thereby urging 

 the blood towards the heart. This, moreover, explains 



