830 THE XERVOUS SYSTEM 



On the left side the nerve is conducted into the thorax in front of the common 

 carotid artery, and crosses in front (or rather to tlie left side) of the arch of the 

 aorta in the interval hetween the trunk of the vagus and its inferior cervical cardiac 

 branch, and ends in the superficial cardiac plexus. 



Middle Cervical Ganglion 



The middle cervical ganglion is a small, somewhat triangular, ganglionic 

 thickening of the cord of the sympathetic. It is situated at the point where the cord 

 crosses the inferior thyrcnd artery at the level of the sixth cervical vertebra. It 

 gives grey rami communicantes to the fifth and sixth cervical nerves. It is 

 connectecl below to the inferior cervical ganglion by the main cord of the s^'mpa- 

 thetic, which passes behind the subclavian artery, and l)y one or more nerve-cords 

 which pass in front of that vessel, forming the ansa Vieussenii. The middle 

 cervical ganglion gives off iDranches to the thyroid l;)ody and the middle cardiac 

 nerve. 



The branches to the thyroid body communicate with the superior cardiac 

 nerve, and proceed to the gland, following the branches of the inferior thyroid 

 artery. 



The middle cardiac nerve enters the thorax, passing sometimes in front of tin- 

 subclavian artery, and sometimes l^ehind that vessel. It communicates in the neck 

 'with the upper cardiac nerve, and in the thorax with the recurrent laryngeal. It 

 terminates in the deep cardiac plexus. On the left side this nerve passes down 

 between the left carotid and subclavian arteries. 



Inferior Cervical Ganglion 



The inferior cervical ganglion is larger than the middle ganglion, and is con- 

 nected by sh(n*t grey rami communicantes to the seventh and eighth cervical 

 nerves. It is irregular in form and is deeply placed, being lodged in a depression 

 between the neck of the first rib and the transverse process of the seventh cervical 

 vertebra. In this situation it is concealed by the vertebral artery, the vessel being 

 placed in front of the ganglion. It is united to the first thoracic ganglion by one 

 or two stout cords and often by a band of ganglionic substance. It gives off 

 branches to the vertebral artery and the inferior cardiac nerve. 



The branches to the vertebral artery are of considerable size and accompany 

 the vessel into the arterio- vertebral foramina in the transverse processes. The 

 plexus thus formed is continued on the vertebral and basilar to the cerebral 

 arteries. 



The inferior cardiac nerve connnunicates with the middle cardiac and recurrent 

 laryngeal, and passes along the side of the trachea to join the deep cardiac plexus. 

 It occasionally arises from the first dorsal ganglion. 



The majority, if not all, of the medullated fibres of the cervical part of the 

 sympathetic cord enter it from the dorsal jiart, to which they pass by the Avhite rami 

 from the upper dorsal ners'es. The destination of many of these fibres is unknown, 

 y)ut some terminate in ramifications round the cells of the upper cervical ganglion 

 and others in a similar manner round the cells of the middle and lower ganglia. 

 The fiV)res which terminate in the upper ganglion are the vaso-motor fibres of the 

 head, the secretory fil^res of the submaxillary glands, the dilator fibres of the pupil, 

 the motor fibres for the smooth muscle of the eyelids and orbit, and the pilo-motor 

 fibres (to the muscles of the hairs) of the face and neck. Those which terminate 

 in the middle and lower cervical ganglia are the cardiac accelerator fibres, and 

 possibly some of the secretory fibres of the sweat glands of the upjier extremity. 



THORACIC PORTION OF THE GANGLIATED CORD 



The thoracic portion of the gangliated cord is represented by a chain of 

 twelve pairs of ganglia. In a few cases, on account of the coalescence of some of 

 the members of the series, the number may be reduced to eleven or ten pairs. The 



