SURGICAL ANATOMY QF SUBMAXILLARY REGION. 71 



readily air may pass into the right "side of the 

 heart, should any one of the larger veins, -or some 

 branch close to the trunk, be divided. 



These several layers of fascia are attached both to the 

 margins of the superior aperture of the thorax and to 

 those structures which pass upwards or downwards 

 through it; and as they are connected together by trans- 

 verse septa, they constitute a species of diaphragm be- 

 tween the cervical and thoracic regions. 



SUKGICAL ANATOMY OF THE STJBMAXILLAKY 

 REGION. 



This region is bounded above by the body of the 

 lower jaw, and the floor of the mouth ; below, by the 

 hyoid bone; externally, by the anterior margin of the 

 sterno-cleido-mastoid muscle. Its surface-markings have 

 been already described (vide Neck). 



Dissection. On reflecting the integument, immedi- 

 ately beneath it, is the subcutaneous cellular tissue, and 

 the fibres of the platysma myoides muscle passing ob- 

 liquely from the jaw towards the chest and shoulder, 

 the a'nterior border of which is free, and separated from 

 its fellow by a cellular interval. Beneath this muscle is 

 a very lax cellular tissue, and on turning it up along 

 the body of the jaw, are seen the nerves supplying it, 

 derived from the facial and upper cervical. A portion 

 of the superior layer of the deep cervical fascia is next 

 met with, attached along the jaw covering in the sub- 

 maxillary gland, and forming the anterior portion of its 

 capsule ; it is continuous externally with the sheath of 

 the sterno-cleido-mastoid, and with the fascia covering 

 the parotid anteriorly. A great many lymphatics lie 



