Chap, ix.] THE CERVICAL FASCIA. 127 



progress of abscesses or growths towards the surface, 

 and would encourage or compel them to take a deeper 

 position. 



(6) The deeper processes. (1) From the super- 

 ficial layer, a process comes off near the anterior 

 border of the sterno-mastoid muscle, which, passing 

 beneath the depressors of the hyoid bone, invests 

 the thyroid body and front of the trachea, and 

 passes down, in front of that tube and of the 

 large vessels, to the fibrous layer of the pericar- 

 dium. (2) The pre vertebral fascia is a layer that 

 descends on the prevertebral muscles behind the 

 pharynx and gullet. It is attached above to the base 

 of the skull, and, below, descends into the thorax, 

 behind the O3sophagus. Laterally, it joins the carotid 

 sheath, and is then prolonged outwards and down- 

 wards over the scalene muscles, the brachial plexus, 

 and subclavian vessels. It follows these vessels 

 beneath the clavicle, where it forms the axillary 

 sheath, and becomes connected with the under surface 

 of the costo-coracoid membrane. (3) The sheath of 

 the carotid artery and its accompanying vein and 

 nerve are derived in part from fascia No. 1, and in 

 part from fascia No. 2. 



The effects of this disposition of the fascia may be 

 illustrated by noting the course probably taken by 

 cervical abscesses in various positions. (1) An abscess 

 in the posterior triangle will be bounded towards the 

 surface by the superficial layer of fascia. Towards 

 tfae floor, or deep part, of the triangle it will be 

 bounded by the lateral portion of fascia No. 2. The 

 abscess may extend some way under the clavicle until 

 arrested by the union of the costo-coracoid membrane 

 with fascia No. 2. It would readily extend under the 

 edge of the trapezius muscle, and could pass beneath 

 the sterno-mastoid muscle and carotid artery to the 

 anterior and deeper parts of the neck. (2) An abscess 



