POSTERIOR TRIANGLE 35 



belly of the omo-hyoid muscle ; indeed, it is the tension of the 

 second layer of the deep fascia which holds the posterior belly of 

 the muscle down in its position (Fig. 51). 



Remove the remaining parts of the deep fascia, first from the 

 upper, and then from the lower part of the triangle, and expose 

 the floor and the remaining contents of the triangle. 



Commence above, in the region of the junction of the upper 

 third and the lower two-thirds of the posterior border of the 

 sterno-mastoid, and secure the great auricular, the lesser occipi- 

 tal and the accessory nerves, and the nervus cutaneus colli. 

 The great auricular is most easily found. It turns round the 

 posterior border of the sterno-mastoid, in the region indicated, 

 and runs upwards and forwards, parallel with and slightly 

 above and posterior to the external jugular vein. The lesser 

 occipital will be found hooking round the lower border of the 

 accessory nerve a little above the great auricular ; and the nervus 

 cutaneus colli lies a little below the great auricular. 



Follow the lesser occipital and the great auricular nerves to 

 their terminations ; but the nervus cutaneus colli must be traced 

 only to the point where it crosses either superficial or deep to 

 the external jugular vein. It eventually divides into upper and 

 lower terminal branches, which will be seen when the anterior 

 triangle is dissected. 



N'ervus Occipitalis Minor. The lesser occipital is a sensory 

 branch of the second cervical nerve. It emerges from under 

 cover of the sterno-mastoid, and ascends for a short distance 

 along its posterior border; then it passes to the superficial 

 surface of the muscle, pierces the deep fascia, and divides 

 into occipital, mastoid, and auricular branches. The occi- 

 pital and mastoid branches supply the skin in the regions 

 indicated by their names. The auricular branch is distributed 

 to the skin of the upper third of the cranial surface of the 

 auricle. 



Nervus Auricularis Magnus. The great auricular nerve v - 

 arises from the second' and third cervical nerves. After 

 turning round the posterior border of the sterno-mastoid, 

 it runs upwards and forwards, on the superficial surface of 

 the sterno-mastoid, towards the angle of the mandible. It 

 breaks up into three sets of terminal cutaneous branches 

 mastoid, auricular, and facial. The mastoid branches go to 

 the skin of the mastoid region. The auricular branches 

 supply the skin of the lower two-thirds of the cranial surface 

 and the lower third of the lateral surface of the auricle. The 

 facial branches, which have already been seen, ramify in the 

 posterior part of the face, in the parotid and masseteric regions. 

 Some of the filaments enter the substance of the parotid 

 gland. 



