584 THE HUMAN BODY. 



though they usually take certain easiest roads. The mam 

 frrain and cord. howpygf, IIP in th 



columns; neiiye-roots, enter the grny mn.^^ grrl froin_fiac]i_ 

 region of the Mtej^m^diill^ 



white column, and_continue_to^ the ^brain.^_Qnce^ in these 

 fibres thejjiipuiae Jhas to keep to a definitely marked out 

 anatomical path, whickJeadsJa. a brain centre or Centres. 

 These paths lie mainly in the lateral columns, the affe- 

 rent (sensory) impulses tending, however, to spread into 

 the posterior columns, and the efferent (volitional) into 

 the anterior; the main bulk of the posterior and anterior 

 columns seems to be made up of commissural fibres join- 

 ing different levels of the cord. The sensory fibres for. the- 

 most part cross soon after they enter the gray matter, and 

 proceed onwards mainly on the side opposite to that of the 

 nerve-root which conveyed them to the cord, while the effe- 

 rent cross mainly in the medulla before they reach the cord; 

 the crossing seems in neither case complete. Hemisection 

 of the cord, therefore, causes marked, but not absoluteness of 

 voluntary movement in muscles of the same side supplied 

 with nerves from a part of the cord below the level of the 

 section; and a considerable, but not complete, loss of sensi- 

 bility on the opposite side. Impulses so powerful as to lead 

 to feelings of pain travel mainly in the gray matter (p. 568), 

 and they also for the most part cross the middle line soon 

 after their entry. 



The Functions of the Brain in General. The brain^ at 

 least in man and _ the-Uiigher -animals^ is the seat of^con- _ 

 j5cjouiies_aiicL jntol 1 i gen p,e ; these disappear when its blood- 

 supply is cut off, as in fainting; pressure on parts of it, as 

 by a tumor or by an effusion of blood in apoplexy, has the 

 same result; inflammation of it causes delirium; and when 

 the cerebral hemispheres are unusually small idiotcy i& 

 observed. .The brain has, however, many other important 

 Junctions; it is the seat of many reflex, automatic, anji 

 co-ordinating centres, which may act as entirely apariirom. 

 consciousness as those of the spinal cord; experiment makes 

 it probable that psychical faculties are dependent on the 

 fore-brain, while the rest of the complex mass has other,. 



