DISSECTION OF THE BACK AND THORAX. 109 



branch from the right vagus, this fusion taking place about the middle 

 of the posterior mediastinum. The lower division unites in the same 

 way with a branch from the nerve of the opposite side, the fusion taking 

 place on the left bronchus. The resulting nerves are termed the 

 styyerior and inferior cesojihageal nerves, and they are continued back- 

 wards, the one above, and the other below, the gullet, giving branches to 

 it and accompanying it through the foramen sinistrum of the dia- 

 phragm. * 



In this part of its coixrse the vagus detaches the following branches : — 



1. A Branch of Communication with the middle cervical ganglion of the 

 sympathetic (or with the inferior ganglion when the middle is not 

 developed). It is given off" within the 1st rib. 



2. The left Inferior {recurrent) Laryngeal Nerve. — This is detached at 

 the root of the posterior aorta ; and turning round behind the vessel at 

 that point, it gains its inner side, to be included between the artery and 

 the left bronchus, where it receives twigs from the cardiac nerves. It 

 then passes forwards along the lower face of the trachea, in company 

 with a cardiac nerve ; and issuing from the chest, it is continued up the 

 neck to the larynx. As it is included between the aorta and left 

 bronchus, it is related to the bronchial lymphatic glands. Within the 

 tliorax the nerve gives branches that pass upwards and forwards to the 

 trachea and oesophagus. The left recui'rent is the nerve implicated in 

 "roaring." 



3. Piilmonary Branches. — These form at the root of the lung a plexus 

 from which filaments are continued into the lung along the ramifications 

 of the air tube. 



Dorsal Roots of the Brachial Plexus. These are two branches of 

 the 1st and 2nd dorsal nerves respectively. They will be found at the 

 upper part of the 1st and 2nd intercostal spaces. After giving branches 

 to the inferior cervical ganglion, they turn round the inner surface of 

 the 1st rib, close to its upper extremity. 



The Sympathetic Nerve. The cervical cord of the sympathetic, 

 which in the neck is fused with the vagus, separates from it at the entrance 

 to the chest, and terminates in a stellate greyish ganglion — tlie middle 

 cervical ganglion. 



The Middle Cervical Ganglion. — This will be found within the 1st rib, 

 or in front of it, at the line of contact of the trachea and oesophagus. 

 A thick connecting branch continues it up to another enlargement — the 

 inferior cervical ganglion. The middle cervical ganglion has a branch 

 of communication witli the vagus, and gives off" two or three cardiac 

 nerves. 



* The superior cesopliageal nerve is generally, if not always, larger than the inferior ; and in most 

 cases I have found that the upper nerve is formed in greater proportion by the left vagus than by 

 the right, while the lower is formed about equally from each. Chauveau, on the other hand, 

 describes and figures the upper nerve as being formed mainly by the right vagus, and the lower by 

 the left vagus. 



