76 



THE HORSE. 



eye, and the faculty of sight is gained ; and a third g'oes to the internal 

 structure of the ear, and the animal hears. Other nerves proceeding to 

 different parts of the head give the faculty of motion to those parts ; and 

 another class bestows the power of feeling. 



One division of nerves (A, p. 68) springing from a prolongation of the 

 brain, and yet within the skull, wander to different 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 involuntary 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 off at certain intervals. 

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



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

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

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

 toward us) proceed from those tracks of the brain devoted to sensation. 

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

 collect together, and passing through a little ganglion or enlargement, c/, 

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

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

 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, 6, pos- 

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

 columns proceed to their destination, enveloped in the same sheath, and 

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

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

 nerve, yet neither their substance nor their ofhce is confounded. Our cut, 

 closely examined, b, will give some idea of the manner in which these 

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

 enveloped in a common 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 sy7n])cdheiic, 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. They go to the heart, and it beats, and to the 

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



