158 STERNO-CLEIDO-MASTOIDEUS. 



Dissection. The dissection of the neck should be commenced by 

 making an incision along the middle line of the neck from the chin 

 to the sternum, and bounding it superiorly and inferiorly by two 

 transverse incisions ; the superior one being carried along the 

 margin of the lower jaw, and across the mastoid process to the 

 tubercle on the occipital bone, the inferior one along the clavicle to 

 the acromion process. The square flap of integument thus included 

 should be turned back from the entire side of the neck, which brings 

 into view the superficial fascia, and on the removal of a thin 

 layer of superficial fascia the platysma myoides will be exposed. 



The platysma myoides (#Xa<ru, (xfc, stdog, broad muscle-like lamella,) 

 is a thin plane of muscular fibres, situated between the two layers 

 of the superficial cervical fascia ; it arises from the integument over 

 the pectoralis major and deltoid muscles, and passes obliquely up- 

 wards and inwards along the side of the neck to. be inserted into 

 the side of the chin, oblique line of the lower jaw, the angle of the 

 mouth, and into the cellular tissue of the face. The most anterior 

 fibres are continuous beneath the chin, with the muscle of the op- 

 posite side ; the next interlace with the depressor anguli oris, and 

 depressor labii inferioris, and the most posterior fibres are disposed 

 in a transverse direction across the side of the face, arising in the 

 cellular tissue covering the parotid gland, and inserted into the 

 angle of the mouth, constituting the risorius Santorini. The entire 

 muscle is analogous to the cutaneous muscle of brutes, the pannicu- 

 lus carnosus. 



Relations. By its external surface with the integument, with 

 which it is closely adherent below, but loosely above. By its internal 

 surface, below the clavicle, with the pectoralis major and deltoid ; 

 in the neck, with the external jugular vein and deep cervical fascia ; 

 on the face, with the parotid gland, the masseter, the facial artery 

 and vein, the buccinator, the depressor anguli oris, and the depres- 

 sor labii inferioris. 



On raising the platysma throughout its whole extent, the sterno- 

 mastoid is brought into view. 



The sterno-cleido mastoid is the largest oblique muscle of the 

 neck, and is situated between two layers of the deep cervical fascia. 

 It arises as implied in its name from the sternum and clavicle 

 (xXsi^i'ov), and passes obliquely upwards and backwards to be inserted 

 into the mastoid process and into the superior curved line of the 

 occipital bone. The sternal portion arises by a rounded tendon, 

 increases in breadth as it ascends, and spreads out to a considerable 

 extent at its insertion. The clavicular portion is broad and fleshy, 

 and separate from the sternal portion below, but becomes gradually 

 blended with its posterior surface as it ascends. 



Relations. By its superficial surface with the integument, the 

 platysma myoides, the external jugular vein, superficial branches of 

 the anterior cervical plexus of nerves, and the anterior layer of the 

 deep cervical fascia. By its deep surface with the deep layer of 

 the cervical fascia ; with the sterno-clavicular articulation, the 

 sterno-hyoid, sterno-thyroid, omo-hyoid, scaleni, levator anguli 



