CRANIAL NERVES. 207 



ous glandular organs, and the contraction of the walls of the stomach and 

 intestines. 



Eleventh Nerve. Spinal Accessory. 



The spinal accessory nerve consists of two distinct portions, the medullary 

 or bulbar, and the spinal. 



Origin. The medullary portion has its origin in nerve-cells in the lower 

 part of the nucleus ambiguus, located beneath the floor of the fourth ven- 

 tricle. From this origin the nerve-fibers pass forward and emerge from the 

 medulla oblongata on its lateral aspect. 



The spinal portion has its origin in the nerve-cells located in the lateral 

 gray matter of the spinal cord as far down as the fifth cervical nerve. From 

 this origin the nerve-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 to form a well-defined nerve. It then passes into the cranial cavity 

 through the foramen magnum and unites with the medullary portion. 



Distribution. After the union the common trunk emerges from the cra- 

 nial cavity through the jugular foramen and after sending branches to the 

 pneumogastric and receiving others in turn from the pneumogastric as well 

 as from the upper cervical nerves it divides into two branches viz.: 



1. An internal or anastomotic branch which soon enters the trunk of the 

 pneumogastric nerve. The fibers of this branch are ultimately distributed 

 to some of the pharyngeal muscles; to all of the muscles of the larynx by 

 way of the laryngeal branches of the vagus nerve, and, according to most 

 authorities, to the heart. 



2. An external branch consisting chiefly of the accessory fibers from the spinal 

 cord. It is distributed to the sterno-cleido-mastoid and trapezius muscles. 



Properties. At its origin it is a purely motor nerve, but in its course it ex- 

 hibits some sensibility, due to the presence of anastomosing fibers. 



Destruction of the medullary root e. g., tearing it from its attachment by 

 means of forceps, impairs the action of the muscles of deglutition and destroys 

 the power of producing vocal sounds from paralysis of the laryngeal muscles, 

 without, however, interfering with the respiratory movements of the larynx, 

 these being controlled by other motor nerves. The normal rate of movement 

 of the heart is increased by destruction of the medullary root. 



Irritation of the external branch throws the trapezius and sternomastoid 

 muscles into convulsive movements, though section of the nerve does not pro- 

 duce complete paralysis, as they are also supplied with motor influence from 

 the cervical nerves. The sternomastoid and trapezius muscles perform move- 



