70 THE HORSE. 



air] tiio faculty of sight is gained ; and a tliird goes to the internal stmc- 

 lure of the ear, and tlie animal hears. Other nerves proceeding to different 

 parts of the head give the faculty of motion to tliose parts ; and another 

 class bestows the power of feeling. 



One division of nerves (A, p. 6S) springing from a prolongation of the 

 brain, and yet within the skull, wander to dillcrent parts of the frame, for 

 important purposes connected with respiration or breathing ; and as the act 

 of breathing is essential to life, and were it to cease, the animal would die 

 — these are nerves of mvolunlary motion ; so that, whether he is awake or 

 asleep, conscious of it or not, the lungs heave and life is supported. Lastly, 

 from the spinal cord, q, (a further prolongation of the brain, and running 

 through a cavity in the bones of the neck, back, and loins, and extending 

 to the very tip of the tail,) other nerves are given olf at certain intervals. 

 This cut delineates one pair of them. The spinal cord, a, is combined of 



six distinct columns or rods, running through its whole length — three on 

 either side. The two columns (the portion of the spinal marrow repre- 

 sented in our cut, is supposed to be placed with its inner or lower surface 

 toward?, us) i)roceed from those tracks of the brain devoted to sensation. 

 From these come out abruptly distinct fibres from the column, and which 

 connect together, and passing through a little ganglion or enlargement, d, 

 (an enlargement of a nervous cord is called a ganglion,) become a nerve 

 of sensation. From the lower or inner side, (a prolongation of tne tracic 

 devoted to motion,) proceed other fibres, which also collect gradually 

 together, and form a nervous cord, c, giving the power of motion. Beyond 

 the ganglion the two unite, and form a perfect spinal nerve, h, possessing the 

 power both of sensation and motion; and the fibres of the two columns 

 proceed ta their destination, enveloped in the same sheath, and apparently 

 one nerve. Each portion, however, continues to be wrapped in its oAvn 

 membrane. They are united, yet distinct; they constitute one nerve, yet 

 neither tli ^ir substance nor their office is confounded. Our cut, closely 

 examined, h, will give some idea of the manner in which these distinct 

 fibres are continued ; — each covered in its own membrane, but all envel- 

 oped ir a connnon covering. 



All these nerves are organs of sensation and motion alone ; but there 

 are others whose origin seems to be outside of and below the brain. These 

 are the sympalheiic, so called from their union and sympathy with all the 

 others, and identified with life itself They proceed from a small ganglion 

 or enlargement in the upper part of the neck, or from a collection of little 

 ganglions in the belly. Tliey go to the heart, and it beats, and to the 

 stomach, and it digests. They form a net-work round each blood-vessel, 



