380 NERVOUS SYSTEM. 
tributed to the pharyngeal muscles and cranial part of the 
cesophagus. 
c. N. laryngeus superior (Z).—This arises from the gan- 
glion nodosum, passes ventrad, crossing the medial surface of 
the carotid artery, and reaches the larynx at about the level 
of the caudal end of M. thyreohyoideus. It passes into the 
larynx and supplies its mucosa. ; 
Thoracic Portion of the Vagus (Fig. 157).—As the vagus 
(2) and sympathetic (c) separate to enter the thorax, the vagus 
(4) lies more ventrad. The right vagus now lies along the 
lateral surface of the trachea, the left one (Fig. 157) along that 
of the cesophagus. At about the level of the first rib or further 
craniad there arise, apparently from the vagus (but really from 
the sympathetic), two slender nerves which pass caudad parallel 
and close to the vagus, lying slightly dorsad of it. These are 
the cardiac nerves (2); they arise from the sympathetic farther 
craniad in the neck region, accompany the vagus, and seem 
to branch from it. In cases where vagus and sympathetic are 
separate throughout their courses, these nerves arise clearly 
from the sympathetic. The cardiac nerves pass to the heart 
and aid in forming a network of nerves known as the cardiac 
plexus (4). 
The vagus usually receives also, at about the level of the 
first rib, one or two communicating branches from the middle 
cervical ganglion (@) of the sympathetic. It then passes to 
the roots of the lungs, crossing the lateral surface of the aortic 
arch on the left side, and the medial surface of the azygos vein 
on the right side. As it crosses the aortic arch the left vagus 
gives off N. laryngeus inferior (7). This curves around 
the caudal side of the aortic arch to the lateral surface of the 
trachea (0), then extends on the lateral and ventral surface of 
the trachea craniad into the neck region. In the neck it passes 
to the dorsolateral side of the trachea and reaches the larynx. 
It passes into the larynx between the cricoid and thyroid carti- 
lages, and supplies the muscles of the larynx. It anastomoses 
with the superior laryngeal. 
The righ¢ inferior laryngeal nerve is given off from the 
right vagus much further craniad than the left; it curves around 
