THE HEAD AND NECK 1235 



The anterior branches are vascular, and pass to the external 

 carotid artery, upon which and its branches they form delicate 

 plexuses. 



Middle Cervical Ganglion. — ^This ganglion is situated opposite 

 the sixth cervical vertebra, and usually lies close to the inferior 

 thyroid artery. It is the smallest of the three, and probably repre- 

 sents two ganglia united into one. Occasionally it is absent. It 

 is connected by grey rami with the fifth and sixth cervical ner\'es, 

 and its branches of distribution are thyroid and middle cardiac. 

 The thyroid branches accompany the inferior thyroid artery to the 

 thyroid body, and they communicate with the external and recur- 

 rent laryngeal nerves. The middle cardiac nerve of each side 

 terminates in the deep cardiac plexus. The nerve of the right side 

 passes either in front of, or behind, the first part of the right sub- 

 clavian artery. It then descends in front of the trachea, and 

 joins the right half of the deep cardiac plexus. The nerve of the 

 left side enters the thorax between the left common carotid and left 

 subclavian arteries, and it joins the left half of the deep cardiac 

 plexus. 



Inferior Cervical Ganglion. — ^This ganglion is situated between the 

 transverse process of the seventh cervical vertebra and the neck 

 of the first rib, where it lies behind the root of the vertebral artery. 

 It is intermediate in size between the superior and middle ganglia, 

 and, like the middle, it probably represents two ganglia united into 

 one. It is frequently fused with the first thoracic ganglion. One 

 or two cords establish a communication between it and the middle 

 cervical ganglion, passing in front of the first part of the subclavian 

 artery. The cord or cords in front of the vessel form a loop around 

 it, called the ansa Vieussenii, or ansa subclavia. The inferior cervical 

 ganglion is connected by grey rami with the seventh and 'eighth 

 cervical nerves, and its branches of distribution are vascular and in- 

 ferior cardiac. The vascular branches accompany the vertebral artery 

 in the form of the vertebral plexus, which gives filaments to the vessel 

 and offshoots along its various branches. The plexus is continued 

 along the basilar artery and its branches, and on to the posterior 

 cerebral arteries. The inferior cardiac nerve on each side joins the 

 deep cardiac plexus. The nerve of the right side passes behind the 

 first part of the right subclavian artery, and then in front of the 

 trachea. It is connected with the middle cardiac and recurrent 

 laryngeal nerves. The nerve of the left side in many cases joins 

 the middle cardiac nerve, and so reaches the deep cardiac plexus. 



Constitution of the Cervical Sympathetic Cord. 



The sympathetic cord in the neck contains the following important groups 

 of fibres, namely, (i) dilator pupillae, (2) vaso-constrictor ajid vaso-dilator, 

 (3) secretory, and (4) accelerator. 



The dilator pupillae fibres axe derived from the upper three thoracic nerves, 

 and ascend in the sympathetic cord to the superior cervical ganglion, in which 

 they terminate. From this ganglion they are continued as sjTnpathetic 



