872 THE NERVOUS SYSTEM. 



arteries have important communications with other nerves. That surrounding the 

 external carotid is connected with the branch of the facial nerve to the stylo-hyoid 

 muscle; that surrounding the facial communicates with the submaxillary ganglion 

 by one or two filaments ; and that accompanying the middle meningeal artery 

 sends offsets which pass to the otic ganglion and to the intumescentiaganglioformis 

 of the facial nerve (external petrosal). 



The Middle Cervical Ganglion (thyroid ganglion} is the smallest of the three 

 cervical ganglia, and is occasionally altogether wanting. It is placed opposite the 

 sixth cervical vertebra, usually upon, or close to, the inferior thyroid artery ; 

 hence the name, "thyroid ganglion," assigned to it by Haller. It is probably 

 formed by the coalescence of two ganglia corresponding to the fifth and sixth cer- 

 vical nerves. 



Its superior branches ascend to communicate with the superior cervical gan- 

 glion. 



Its inferior branches descend to communicate with the inferior cervical ganglion. 



Its external branches pass outward to join the fifth and sixth spinal nerves. 

 These branches are -not constantly found. 



Its internal branches are the thyroid and the middle cardiac nerve. 



The thyroid branches are small filaments which accompany the inferior thyroid 

 artery to the thyroid gland ; they communicate, on the artery, with the superior 

 cardiac nerve, and, in the gland, with branches from the recurrent and external 

 laryngeal nerves. 



The middle cardiac nerve (nervus cardiacus magnus), the largest of the three 

 cardiac nerves, arises from the middle cervical ganglion or from the cord between 

 the middle and inferior ganglia. On the right side it descends behind the common 

 carotid artery, and at the root of the neck passes either in front of or behind the 

 subclavian artery; it then descends on the trachea, receives a few filaments from 

 the recurrent laryngeal nerve, and joins the deep cardiac plexus. In the neck it 

 communicates with the superior cardiac and recurrent laryngeal nerves. On the 

 left side the middle cardiac nerve enters the chest between the left carotid and sub- 

 clavian arteries, and joins the left side of the deep cardiac plexus. 



The Inferior Cervical G-anglion is situated between the base of the transverse 

 process of the last cervical vertebra and the neck of the first rib on the inner side 

 of the superior intercostal artery. Its form is irregular; it is larger in size than 

 the preceding, and frequently joined with the first thoracic ganglion. It is proba- 

 bly formed by the coalescence of two ganglia which correspond to the two last 

 cervical nerves. 



Its superior branches communicate with the middle cervical ganglion. 



Its inferior branches descend, some in front of, others behind, the subclavian 

 artery, to join the first thoracic ganglion. 



Its internal branch is the inferior cardiac nerve. 



The inferior cardiac nerve (nervus cardiacus minor) arises from the inferior 

 cervical or first thoracic ganglion. It passes down behind the subclavian artery 

 and along the front of the trachea to join the deep cardiac plexus. It communi- 

 cates freely behind the subclavian artery with the recurrent laryngeal and middle 

 cardiac nerves. 



The external branches consist of several filaments, some of which communi- 

 cate with the seventh and eighth spinal nerves ; others accompany the vertebral 

 artery along the vertebral canal, forming a plexus round the vessel, supplying it 

 with filaments, and communicating with the cervical spinal nerves as high as the 

 fourth. 



Thoracic Portion of the Gangliated Cord. 



The thoracic portion of the gangliated cord consists of a series of ganglia 

 which usually correspond in number to that of the vertebrae, but, from the occa- 

 sional coalescence of two, their number is uncertain. These ganglia are placed 

 on each side of the spine, resting against the heads of the ribs and covered by the 



