786 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



groups of muscles, which must in their contraction follow each other in a 

 certain definite sequence; so, also, the act of coughing requires the associa- 

 tion of a number of different muscular movements. Numerous other illus- 

 trations might be given of the combination of complex movements which 

 are governed by so-termed co-ordinating centres ; that is, a collection of 

 ganglia located, usually, in the spinal cord or medulla oblongata which 

 govern certain specific movements. 



V. THE FUNCTIONS OF THE SPINAL CORD. 

 The spinal cord is contained within the vertebral canal and is com- 

 posed of white matter externally and gray matter internally, inclosed in 

 membranous sheaths of which the pia mater is adherent to the white 



A A 



p P P P 



Fig. 332.— Tkassvebse Section of the Spinal Cord. (Lantlois.) 



In the centre is the butterfly-form of the gray matter surrounded by white matter, p, posterior, and 

 a, anterior horns of the gray matter; PR posterior roots, AR anterior roots of a spinal nerve; A A 

 the white anterior, L L the lateral, P P the posterior columns. 



matter ; externally is found the dura mater, which lines the vertebral 

 canal and forms a protective coat for the cord, while between the two is 

 found the arachnoid membrane. 



The white matter of the spinal cord is composed of nerve-fibres 

 arranged longitudinally and divided into the so-called anterior, lateral, 

 and posterior columns by the passage of the roots of the spinal nerves. 

 The anterior fissure is a depression which separates the two anterior 

 columns of the cord, which are bounded, therefore, on one side by the 

 fissure and on the other by the points of origin of the anterior spinal 

 nerve-roots. 



The anterior fissure does not extend down to the gray matter, which 

 composes the centre of the cord, but is separated from it by the white 

 commissure. 



