382 NERl^OUS SYSTEM. 



the right subclavian artery just caudad of the origin of the 

 internal mammary artery, then passes to the trachea, and has 

 a course and distribution like that of the left side. 



On reaching the root of the lungs the vagus divides into 

 numerous branches which form the pulmonary plexus {k) over 

 the roots of the lungs, and extends onto the basis of the heart 

 as the cardiac plexus. From these plexuses numerous 

 branches pass to the heart, lungs, pulmonary artery, pericar- 

 dium, etc. The cardiac branches from the sympathetic, men- 

 tioned above, are also connected with the cardiac plexus. 



Caudad of the pulmonary plexus the vagus is continued 

 on each side as two trunks, a dorsal (;//) and a ventral (/) 

 which pass along the oesophagus (/>). The ventral branches 

 of right and left vagi (/and /') unite a short distance caudad 

 of the root of the lung, and the single trunk extends into the 

 abdominal cavity on the ventral surface of the oesophagus. 

 The dorsal branches of right and left vagi unite farther back, 

 near the diaphragm, and the single trunk thus formed {in) 

 enters the abdominal cavity on the dorsal surface of the 

 oesophagus. Both divisions give fine nerves to the oesophagus. 



Abdominal Portion of the Vagus (Fig. 164, page 407). — 

 After passing through the diaphragm the ventral division (Fig. 

 164, /) reaches the lesser curvature of the stomach (1), over 

 which it ramifies, some branches being traceable almost to the 

 pylorus. The network of branches thus formed is the anterior 

 gastric plexus. Some twigs from the ventral division pass 

 transversely across the cranial end of the stomach and join the 

 plexus formed by the dorsal division. 



The dorsal division (;;/) of the vagus reaches the greater 

 curvature of the stomach, where it ramifies, forming the pos- 

 terior gastric plexus. Branches from this anastomose with 

 the anterior gastric plexus and with the coeliac plexus of the 

 sympathetic {e). 



XI. N. ACCESSORIUS. — The accessory (or spinal accessory) 

 nerve arises (Fig. 138, AY) by numerous rootlets from the 

 lateral surface of the medulla and of the spinal cord as far 

 caudad as the fifth to seventh cervical nerve. These spinal 

 rootlets join to form a nerve which enters the cranium through 



