THE CRANIAL NERVES 



655 



the organs innervated by it, it may be stated at this time that it is 

 primarily concerned with respiration, the action of the heart, and the 

 musculomotor and secretomotor processes of the digestive organs. 



(a) Respiration. It supplies motor fibers to the muscles of the larynx, trachea 

 and bronchi. The most important nerves to be mentioned in this connection are 

 its superior and inferior laryngeal branches. It also serves as the sensory nerve 

 of the larynx (sup. laryngeus) and the lungs. The latter are directly concerned 

 with the self-regulation of respiration. 



(6) The Heart. The vagus conveys inhibitor impulses to this organ, and also 

 sensory impulses from this region by way of its "depressor fibers." 



ycuLA 



vagus] 



\ 



ARCUATE 

 NUCLEUS 



XII. 

 [HYPOGLOSSAL] 



FiQ. 327. 



-Cross-section of Medulla Showing Nuclei of Nerves x and xii. 

 (Cunningham.) 



(c) Digestive Organs. The vagus innervates the sphincters of the pharynx 

 and the musculature of the esophagus, stomach and intestine. It sends secreto- 

 motor fibers to the stomach, intestine, pancreas and possibly also to other abdom- 

 inal organs. The vasomotor mechanisms of these organs are supplied with fibers 

 from the solar plexus. While the latter in turn communicates with the thoracic 

 sympathetic system through the splanchnic nerves, it is also intimately connected 

 with the vagus system. 



11. The accessory nerve is formed from several upper roots which 

 take their origin in the medulla, and from a series of lower roots which 

 arise from the anterior gray matter of the spinal cord as low as the 

 fifth to seventh cervical vertebrae. It is a motor nerve and suppHes 

 the sternocleidomastoid and trapezius muscles. 



