124 



THE HEAD AND NECK 



parotid gland, in the upper part of its course, and it descends 

 between the internal jugular vein and the internal carotid 

 artery. It appears at the lower border of the posterior belly 



of the digastric, and 

 bends forwards almost 

 at right angles, hooking 

 round the occipital artery. 

 It crosses superficial to 

 the internal and external 

 carotid arteries and to 

 the loop formed by the 

 lingual, and it is itself 

 crossed by the lingual 

 veins. It runs forwards, 

 a little above the level 

 of the hyoid bone, and 

 disappears under cover 

 of the posterior belly of 

 the digastric (Fig. 39). 

 It reappears above the 

 common tendon of the 

 digastric, lying on the 

 hyo-glossus. On reach- 

 ing the posterior border 

 of the mylo-hyoid, the 

 nerve enters the inter- 

 muscular space between 

 this muscle and the hyo- 



FlG. 40. Diagram to illustrate the Path of gloSSUS (p. 154), and SO 



the Efferent Fibres from the Central reac h eS the muscles of 



Nervous System to the Sympathetic ^ , . , . 



Ganglia. The cervical and the upper the tongue, which it SU P - 



portion of the thoracic part of the sym- plies. In the Superficial 



pathetic trunk are shown. In the cervical par O f fts course it gives 



region, grey rami communicantes alone _. , ,. , * 



are present, but in the thoracic region ot a descending branch 



white rami communicantes are present in (p. 154) and the nerve 



addition. The posterior rami (primary Q f supp ly to t he thyreo- 



divisions) of the spinal nerves are not , . , 



shown in the diagram. 



hyoid. 



The Sympathetic 

 Trunk in the neck is embedded in the posterior wall of the 

 carotid sheath, and lies posterior to the common and internal 

 carotid arteries and medial to the vagus nerve. It possesses 

 three ganglia, and these send afferent fibres to the spinal 



