76 SURGICAL ANATOMY OF 



Dissection. On the removal of the integument, the 

 subcutaneous cellular tissue is first met with, and the 

 anterior portion of the platysma, which is usually un- 

 connected with its fellow of the opposite side, there 

 being a cellular interval between them, well marked in 

 the necks of old people when the fat is absorbed, caus- 

 ing the " dewlap " appearance characteristic of age. 

 Beneath these muscular fibres is a thin layer of cellular 

 tissue, which allows of the free movements of the in- 

 tegument and platysma over the underlying aponeurotic 

 sheaths of the muscles. Along the anterior border of 

 the sterno-mastoid is the anterior jugular vein, which, 

 however, is at times absent. The sterno-hyoid and 

 omo-hyoid muscles themselves form the next layer, in 

 their aponeurotic sheaths, and immediately below them 

 lie the sterno-thyroid and thyro-hyoid muscles. The 

 sterno-hyoid muscles pass somewhat obliquely, so that 

 the interspace between their internal free borders is 

 rather wider towards the sternum than at the hyoid 

 bone ; whilst the inner margins of the sterno-thyroids 

 are slightly oblique in the opposite direction. 



The nerves supplying these muscles are seen gener- 

 ally on their posterior borders, or ramifying upon them. 

 Beneath the muscles just named, in the mesial line, 

 from above downwards, are met with (1) the hyoid 

 bone; (2) the thyro-hyoid membrane; (3) the thyroid 

 cartilage ; (4) the crico-thyroid membrane ; (5) the cri- 

 coid cartilage, partly covered by the crico-thyroid mus- 

 cle ; (6) the first ring or two of the trachea ; (7) the thy- 

 roid body and its isthmus extending between the lobes ; 

 (8) the trachea (passing backwards and downwards to- 

 wards the thorax), upon which lies a plexus of veins, 

 the inferior and middle thyroid, passing downwards 



