THE NERVOUS SYSTEM 227 



Tenth Pair. The Pneumogastric Nerves 



They are the longest and most widely distributed of all the 

 cranial nerves. It goes to the pharynx, oasophagus, stomach, 

 liver, intestines ; to the larynx, trachea, lungs, and heart. 



Eleventh Pair. The Spinal Accessory Nerves 



As its name implies, this nerve received a part of its origin 

 from the spinal cord, in the cervical region. A portion of it 

 is incorporated in the vagus, and the other part supplies cer- 

 tain muscles of the neck and chest. Some of its fibres entirely 

 control the power of the vocal chords to produce sounds. 



Twelfth Pair. The Hypoglossal Nerves 

 Its only function is the control of the motions of the tongue. 



15. The Spinal Cord. The spinal cord, or " marrow," is a 

 cylindrical mass of soft nervous tissue, which occupies a 

 chamber, or tunnel, fashioned for it in the spinal column 

 (Figs. 58 and 59). It is composed of the same substances 

 as the brain; but the arrangement is exactly reversed the 

 white matter encompassing or surrounding the gray matter, 

 instead of being encompassed by it. The amount of the white 

 substance is also greatly in excess of the other material. A 

 vertical fissure partly separates the cord into two lateral halves, 

 and each half is composed of two separate bundles of fibres, 

 which are named the anterior and posterior columns. 



16. These columns have entirely different uses, and each of 

 them unites with a different portion of the nerves which have 

 their origin in the spinal cord. The importance of this part 

 of the nervous system is apparent from the extreme care taken 



What is stated of the pneumogastric nerves ? The spinal accessory nerves ? The 

 hypoglossal nerves ? 



15. Describe the composition of the spinal cord. What space does the spinal cord 'oc- 

 cupy ? In what respect does the substance composing the spinal cord and the substance 

 composing the brain agree ? In what respect do they differ? Does white or gray matter 

 predominate in the spinal cord ? In the brain ? How is the spinal cord divided ? Compo- 

 sition of each half ? Names ? 



16. Uses of these columns ? Importance of this part of the nervous system ? How 

 protected ? The three membranes that cover the brain ? _ 



