264 



A Manual of Veterinary Physiology. 



the inferior portion of the inverted comma, or, as we shall 

 speak of it, the inferior cornu, they are exceedingly 

 numerous, there being five groups of nerve cells each 

 known by a separate name ; whilst the cells of the superior 

 cornu are not onl}- fewer in number, but the number of 

 groups is only three or four. 



Tracts in the Cord. — The white matter of the cord can 

 be mapped out into columns or tracts, which are quite 

 distinct from the columns into which the cord is originally 



Fig. 25.— DiAtiRAM to Illustrate the General Arrangement 

 of the Several Tracts op White Matter in the Spinal 



Cokd. 



The ascending tracts are shaded with dots ; the descending tracts art- 

 shaded with lines. The shading is in each case put on one sid< 

 of the cord only, the reference letters beiDg placed on the other 

 side. cr.i>, pyramidal tract; di\, direct pyramidal tract: C.b., 

 cerebellar tract ; s.l.r. and c.r. together indicate the median 

 posterior tract (tract of the fibres of the superior or sensory roots 

 of the spinal nerves) ; asc.a.l., the antero-lateral ascending tract : 

 desc.l., the antero-lateral descending tract. (Foster, after Sher- 

 rington.) 



divided. Some of these tracts are supposed to be convey- 

 ing impulses from the cord to the brain, and are known 

 as ascending tracts ; others are convoying impulses from 

 the brain to the cord, and arc known as descending tracts. 

 These descending and ascending tracts have not been mad< 

 out by ordinary observation, but by experimental inquiry 

 Tt was found that, after division of certain nerves or injuries 

 to certain parts of the brain, particular tracts became do- 



