552 THE NERVES. 



nucleus of the spinal marrow, as a series of spinal ganglia, 

 (found in the lower animals to consist of separate 

 knots,) whose office in particular it is, to preside over the 

 sensations and voluntary motions of the limbs and body ; the 

 ganglia of the sympathetic nerve, having mainly under their 

 control the peculiar sensations and involuntary motions of the 

 visceral organs. 



Of the Medullary Neurine forming the Commissures. 



White bands of medullary neurine are found in many por- 

 tions of the cerebro-spinal system, passing from side to side 

 between symmetrical ganglia, (arising from one, so far as we 

 can carry our investigation, and terminating in the other,) which 

 are called commissures, and whose office it appears to be, to 

 attach together these different organs so as to give to them a 

 certain sort of unity in their operations. 



We have one instance of the many commissures that exist, 

 in the corpus callosum, which is extended across between the 

 two hemispheres of the cerebrum, at the only place where they 

 can come in contact, immediately below the falx major ; and 

 another in the white fasciculi that pass across from the cere- 

 bellum over the pons varolii, (see fig. 224, page 577,) and meet 

 with those of the opposite side on the middle line of the pons. 

 These constitute the great commissures or bonds of union of 

 the two sides of the cerebrum and cerebellum. 

 In the ganglia of the sympathetic, parts of the fibres of the 

 evident white cords connecting the ganglia together, are 

 believed, by Solly, to belong to the system of commissures. 



Of the Nerves. 



The means by which the ganglia are placed in connexion 

 with the organs of sense, the skin, muscles, and other portions 

 of the body, are the thousands of white medullary filaments, 

 which, shortly after their origin from the central parts of the 

 nervous system, pass out among the other tissues of the body, 

 where they are rolled up into cylindrical cords and receive the 

 name of nerves. These, for the purposes of greater clearness 

 in description, are represented as dependencies of the central 



