

THE HEAD AND NECK. 45 



SPECIFIC BOUNDARIES OF CERVICAL TRIANGLES. (Fig. 23.) 



1. Digastric Triangle. Mandible and masto-mandibular line ; anterior belly 

 of digastric muscle ; posterior belly of digastric muscle and stylo-hyoid muscle. 



2. Superior Carotid Triangle. Sterno-cleido-mastoid muscle ; anterior belly 

 of omo-hyoid muscle ; stylo-hyoid muscle and posterior belly of digastric muscle. 



3. Inferior Carotid or Traclieal Triangle. Mid mento-sternal line ; sterno- 

 cleido-mastoid muscle ; anterior belly of omo-hyoid muscle. 



4. The Occipital Triangle. The trapezius muscle; the posterior belly of the 

 omo-hyoid muscle ; the sterno-mastoid muscle. 



5. 'The Subclaman Triangle. The clavicle ; the posterior belly of the omo- 

 hyoid muscle ; the sterno-cleido-mastoid muscle. 



Note that the sterno-mastoid divides the neck into two triangles. Of these 

 two the anterior contains three, the posterior two, smaller triangles. 



Dissection to sJwiv superficial structures in the superficial fascia of tJie neck, 

 as follou'S : 



1 . The platysma myoides muscle a dermal. 



2. The anterior jugular vein is in front of sterno-mastoid. 



3. The posterior jugular vein is behind the sterno-mastoid. 



4. External jugular vein crosses the sterno-mastoid. 



5. The superficial lymphatics vertical group. (Fig. 23.) 



6. The superficial lymphatics transverse group. (Fig. 23.) 



7. The inframandibular branch of the seventh nerve. (Fig. 22.) 



8. The superficial cervical nerve, of cervical plexus. (Fig. 22.) 



9. The great auricular nerve, of cervical plexus. (Fig. 22.) 



10. The small occipital nerve, of cervical plexus. (Fig. 22.) 



11. The suprasternal nerve, of cervical plexus. (Fig. 22.) 



12. The supraclavicular nerve, of cervical plexus. (Fig. 22.) 



13. The supraacromial nerve, of the cervical plexus. (Fig. 22.) 



The platysma myoides (Fig. 14) is a dermal muscle. It is allied to the 

 muscles of expression and to the three dermal aural muscles ; they are all rem- 

 nants in man of the great panniculus carnosus. To expose this muscle it will 

 be necessary to exercise the greatest care in removing the skin. Usually the 

 fibres of origin of this muscle extend two .inches below the clavicle. They are 

 continued obliquely upward and forward onto the face. In some persons this 

 muscle is very heavy ; in others it is almost absent. 



The Superficial Nerves of the Cervical Plexus and the Spinal Accessory 

 Nerve. Dissection. Locate the posterior border of the sterno-cleido-mastoid 

 muscle. Very carefully cut the platysma along this posterior border, using the 

 forceps for a director. Next cut through the deep fascia along the posterior border 

 of the muscle. Now look first for a small nerve that parallels the posterior border 

 of the sterno-cleido-mastoid muscle. (Fig. '22. ) This is the lesser occipital. 

 Trace it upward, as in the figure. 



Three nerves cross the sterno-cleido-mastoid: (i) The mastoid branch, or 

 second small occipital ; (2) the great occipital ; (3) the superficial cervical. 



Follow their branches out, taking care to harm no veins. These are the 

 three ascending branches of the plexus. 



The spinal accessory nerve is sometimes the subject of surgical procedure. 

 On the living, if you are in doubt as to whether you have the spinal accessory 

 or some other nerve, remember this rule : Pinch the nerve with the forceps, and 

 if it is the spinal accessory you have, the trapezius muscle will elevate the 

 shoulder-blade. The other nerves that this one is sometimes mistaken for are 

 all sensory, and will, if pinched, produce no muscular contraction. 



