272 A Manual of Veterinary Physiology. 



in an exact and regular order is essential, and the same 

 remark applies to swallowing, and the muscles used in 

 respiration and other similar acts. 



Conducting Paths in the Cord. — We must now examine 

 the paths by which impressions are conveyed between the 

 body and the brain, and vice versa. 



Sensory impressions enter the cord at the superior roots, 

 and pass for a short distance along the superior columns ; 

 they then enter the grey matter, passing through the gan- 

 glion cells, and cross to the opposite side of the cord (Fig. 26) ; 

 from here they pass once more into the white substance. 

 It is supposed that, depending on the nature of the impres- 

 sion, the path by which it enters the brain varies, pain 

 being conveyed by one of the white lateral tracts of the 

 cord ; touch, temperature, pressure, and muscular sensi- 

 bility by one of the superior tracts. In this way the impres- 

 sion passes along the cord on the opposite side (excepting 

 muscular sensibility, which is on the same side) to that on 

 which it entered, and so enters the brain. Here the im- 

 pression is made and a motor impulse is generated, which, 

 passing out of the brain into the medulla, crosses over either 

 in this or the pons, and passing down the pyramidal tracts 

 joins the motor or inferior spinal root (Fig. 26) ; some sensory 

 impressions instead of crossing in the medulla cross in the 

 cord. The conductors of muscular sense, besides travelling 

 up the same side of the cord on which they entered, do not 

 decussate in the cord but in the medulla. Complex co- 

 ordinated movements are supposed to be capable of being 

 set up in the grey matter of the inferior cornu, either in 

 response to an impression from the brain, or as a reflex ad 

 lii-oiight about by the sensory nerves passing to the cord. 



Having learned the arrangement of the nerves and spinal 

 cord and the functions of nerve centres, we have next to 

 consider the functions of the spinal cord itself. 



The Functions of the Spinal Cord are to transmit motor 

 and sensory impulses between the body and the brain, not 

 only up and down the cord, hut from side to side. It is 

 the chief centre of reflex actions, both with and without 



