170 THE NERVOUS SYSTEM. 



body; and we are thus left to direct the attention, the rea- 

 son, and the will to the accomplishment of the great ends 

 of our existence. If it were otherwise, w r e could only find 

 time to attend to our ordinary physical wants. 



46. The objects of the reflex activity of the cord are 

 threefold. In the first place, it acts as the protector of man, 

 in his unconscious moments. It is his unseen guardian, 

 always ready to act, never growing weary, and never re- 

 quiring sleep. Nor does its faithful action wholly cease 

 with the cessation of life in other parts. In the second 

 place, it is the regulator of numerous involuntary motions 

 that are necessary to the nutrition of the body. Here its 

 actions are entirely independent of the brain, and are per- 

 formed in a secret and automatic manner. And. thirdly, it 

 acts as a substitute, and regulates involuntary movements 

 in the muscles usually under the influence of the will. It 

 thus takes the place of the higher faculties in performing 

 habitual acts, and permits them to extend their operations 

 more and more beyond the body and its material wants. 



47. The Functions of the Medulla Oblongata. 

 The prolongation of the spinal cord, within the skull, 



has been previously spoken of as the medulla oblongata. 

 It resembles the cord, in being composed of both white 

 and gray matter, and in conducting sensory and motor in- 

 fluences. It likewise gives rise to certain nerves, which are 

 here called cranial nerves (from cranium, the skull). All 

 except two of these important nerves spring from the me- 

 dulla, or the parts immediately adjoining it ; the exceptions 

 are the two nerves taking part in the special senses of sight 

 and smell, which nerves have their origin at the base of 

 the cerebrum. 



48. The decussation, or crossing of the motor columns, 

 has been previously described, when treating of the direc- 



46. How many objects may the reflex activity be said to have ? State the first. 

 The second. The third. 



47. How does the medulla oblongata resemble the cord ? 



48. What final fact is observed in the crossing of the motor columns ? 



