604 TEXT-BOOK OF PHYSIOLOGY. 



nerve excites contraction of the upper part of the small intestine and of the 

 gall-bladder, the secretion of the pancreas, the renal circulation, the secretion 

 of urine, etc. 



Functions. The afferent fibers transmit nerve impulses from the area 

 of their distribution to the medulla and thence through cortical connections 

 to the sensor cerebral areas, where they evoke sensations. They therefore 

 endow all parts to which they are distributed with sensibility. 



The efferent fibers transmit impulses outward which excite contraction 

 of the muscle of the lower two-thirds of the esophagus, the stomach, the 

 small intestine, and the gall-bladder, and the muscles of the bronchial tubes; 

 excite secretion from the glands of the stomach, pancreas, and kidney, and 

 exert an inhibitor influence on the activity of the heart. The efferent fibers 

 belong to the autonomic system of nerves and are not connected with the 

 ganglia of the vagus, but with local peripheral ganglia. 



The afferent fibers also assist in the maintenance of certain organic 

 reflex actions which are highly essential to the life of the individual, e.g., 

 respiration, the heart-beat, blood-pressure, etc., all of which have been con- 

 sidered in foregoing pages. 



ELEVENTH NERVE. THE SPINAL ACCESSORY. 



The eleventh cranial nerve, the spinal accessory, consists of peripherally 

 coursing fibers which bring the nerve-cells from which they arise into relation 

 with separate but functionally related muscles, such as those entering into 

 the formation of the larynx. It consists of two portions, the medullary or 

 bulbar and the spinal. 



Origin. The axons comprising the medullary portion arise from a group 

 of nerve-cells in the extreme lower part of the nucleus ambiguus, known as the 

 nidus laryngei. From this origin the axons pass forward and outward to 

 emerge from the medulla just below and in series with the roots of the vagus 

 nerve. 



The axons comprising the spinal portion have their origin in nerve-cells 

 in the lateral margin of the anterior horn of the gray matter in the cervical 

 portion of the cord as far down as the fifth cervical vertebra. From this 

 origin the fibers pass to the surface of the cord to emerge between the ventral 

 and dorsal roots in from six to eight filaments, after which they unite from 

 below upward to form a distinct nerve. This enters the cranial cavity 

 through the foramen magnum, where it joins with the medullary portion to 

 form the common trunk, which then passes forward to emerge from the 

 cranium through the jugular foramen. (Fig. 281.) 



Distribution. After emerging from the cranial cavity the nerve soon 

 separates into two branches: 



i. An internal or anastomotic branch, consisting chiefly of filaments coming 

 from the medulla oblongata. It soons enters the trunk of the vagus, 

 from which fibers pass through the pharyngeal plexus to the superior and 

 inferior constrictor muscles of the pharynx, to the palato-pharyngeus, 

 to the levator palati and azygos uvulae muscles (Beevor and Horsley) ; to 

 the muscles of the larynx through the inferior laryngeal nerve, and to the 

 heart according to some authorities. 



