THE NERVOUS SYSTEM. 1?1 



tion of the nerve-fibres of the cord ; and the singular fact 

 has been alluded to, that when one side of the brain is 

 injured, its effects are limited to the opposite side of the 

 body. One more fact remains to be observed in this con- 

 nection, namely, this crossed action does not usually take 

 place in the cranial nerves. Accordingly, when apoplexy, 

 or the rupture of a blood-vessel, occurs in the right hemi- 

 sphere of the cerebrum, the left side of the body is paralyzed, 

 but the right side of the face is affected; this is because 

 that part of the body is supplied by the cranial nerves. 



49. A portion of the medulla presides over the impor- 

 tant function of respiration, and from it arises the pneu~ 

 mogastric nerve, so called because its branches serve both 

 the lungs and stomach. The feelings of hunger, thirst, 

 and the desire for air are aroused by means of this nerve. 

 The wounding of the gray matter of the medulla, even of 

 a small portion of it, near the origin of the pneumogastric 

 nerve, at once stops the action of the lungs and causes 

 death. In consequence of the importance of this part, it 

 has been termed the "vital knot." We find, also, that its 

 location within the skull is exceedingly well protected, it 

 being quite beyond the reach of any ordinary form of 

 harm from without. 



50. The Functions of the Cranial Ganglia. The 

 uses of the smaller gray masses lying at the basv. of the 

 brain are not well ascertained; and, on account of their 

 position, so remote from the surface, it would, at first, seem 

 well-nigh impossible to study them. But, from the results 

 following diseases in these parts, and from experiments 

 upon inferior animals, they are becoming gradually better 

 understood; and there is reason to believe that eventually 

 the physiological office of each part will be clearly ascer- 

 tained and defined. It is believed, however, but not abso- 



49. The pneumogastric nerve? The feelings aroused by it? The "vital 

 knot?" 



50. The uses of the smaller gray masses at the base of the brain ? 



