J 3^2 HUMAN ANATOMY. 



ff. The branches to the pituitary body consist of several tiny filaments which enter the 

 substance of that body. 



4. The vertebral branches consist of two or three filaments which pass 

 backward, pierce the prevertebral muscles and are distributed to the bony and liga- 

 mentous structures of the upper portion of the vertebral column. 



The Middle Cervical Ganglion. — The middle cervical ganglion (g. cervicale 

 medium), a structure not infrequently absent, consists of one or two collections 

 of nerve-cells situated posterior to the carotid sheath in the neighborhood of 

 the inferior thyroid artery (Fig. 1131). It lies about the level of the sixth cervical 

 vertebra and represents the fusion of two primitive cervical ganglia. 



The somatic branches are : (i) the gray rami cotnmunicantes and (2) the 

 subclavian loop. 



1. The gray rami communicantes arise either from the ganglion or from its 

 upper or lower association cord. They consist of two trunks which pass backward 

 and join the anterior primary divisions of the fifth and sixth cervical nerves. 



2. The subclavian loop (ansa subclavia [Vieussenii] ) is a nerve, frequently 

 double, which passes over the subclavian artery and joins the inferior cervical gang- 

 lion sending twigs (plexus subclavius) to the subclavian artery and its branches and 

 to the phrenic nerve. 



The visceral branches are: (i) the thyroid plexus and (2) the iniddle 

 cervical cardiac nerve. In case of absence of the middle cervical ganglion, these 

 branches arise from the interganglionic association cord between the superior and 

 inferior ganglia. 



1. The thyroid plexus (plexus thyreoideus inferior) consists of several fine 

 inosculating twigs which accompany the inferior thyroid artery into the substance 

 of the thyroid body. 



2. The middle cervical cardiac nerve (a. cardiacus medius) (Fig. 1131) 

 differs in its course on the two sides of the body. Descending in the neck, where 

 it inosculates with the superior cervical cardiac and inferior laryngeal nerves, it 

 passes, on the right side, either anterior or posterior to the subclavian artery, to 

 the front of the trachea where it receives filaments of inosculation from the inferior 

 laryngeal nerve. On the left side it enters the thorax between the common carotid 

 and subclavian arteries. On both right and left sides it terminates posterior to the 

 arch of the aorta by entering corresponding sides of the deep cardiac plexus. 



Variations. — The gangliated cord, in the region of the middle ganglion, may lie posterior 

 to the inferior thyroid artery or may be bifurcated, the artery lying between the two portions. 



The Inferior Cervical Ganglion. — The inferior cervical ganglion (g. cervicale 

 inferius) (Fig. 1079) is situated at the root of the neck, over the first costo-central 

 articulation, between the neck of the first rib and the transverse process of the 

 seventh cervical vertebra. In shape it is irregular, being flat, round or cres- 

 centic, and it is often fused with or only partially separated from the first thoracic 

 ganglion. Situated in the external angle between the subclavian and vertebral 

 arteries it is usually connected above with the middle ganglion by an association cord 

 and by the subclavian loop, the former, passing posterior to the vertebral artery, 

 but sometimes, especially on the left side, forming a nervous ring aroimd that vessel. 



The somatic branches consist of: (i) the gray rami communicantes., (2) the 

 subclaviaji loop and (3) a communicating branch to the inferior laryngeal nerve. 



1. The gray rami communicantes consist of two nonmeduUated trunks 

 which join the anterior primary divisions of the seventh and eighth cervical nerves. 



2. The subclavian loop (ansa subclavia [Vieussenii] ) has already been de- 

 scribed, as a branch of the middle cervical ganglion. 



3. The communicating branch to the inferior laryngeal nerve frequently 

 accompanies the inferior cervical cardiac nerve ; it joins the inferior laryngeal pos- 

 terior to the subclavian artery. 



The visceral branches comprise : (i) the vertebral plexus 2inA (2) the itiferior 

 cervical cardiac nerve. 



