CHAPTER IV. 

 THE NERVOUS SYSTEM. 



THIS system is a very important set of organs controll- 

 ing the motion of the various members of the body 

 and supplying the different senses of feeling, seeing, 

 hearing, smelling and tasting. The two principal 

 organs of the nervous system are the brain and the spinal 

 cord. 



1. The Brain. — The brain is the centre of the whole ner- 

 vous system, and is situated in the cranial cavity, surrounded 

 by three delicate membranes, the outer one being attached 

 to the inner wall of the cranial cavity. It contains several 

 important nerves called the cranial nerves, which are given 

 off from the brain and passed down through the various 

 foramen or openings in the head to supply the different or- 

 gans situated there. The optic nerve passes down to the eye, 

 giving the sense of sight. The auditory nerve passes down 

 to the drum of the ear to give the sense of hearing. The 

 aulfactory nerves, which give the sense of smell, are situated 

 in the mucous membrane lining the nose. The nerves passing 

 down to the tongue give the sense of taste. Other nerves 

 pass down to the lips, teeth, mouth and face, giving motion 

 and feeling to the parts mentioned. Others pass down to 

 the gullet or pharynx, giving it the power of swallowing. 



2. The Spinal Cord. — Passing from the spinal cord, which 

 is situated in the opening of the bones of the back, are 

 numerous small nerves to supply the muscles of the neck, 

 giving it motion and feeling. Nearly opposite the shoulder 

 blade, or withers, the spinal cord gives off a large bunch 

 of nerves, part of which supplies the heart and lungs with 

 nervous power. This is a point of importance, for if the 

 spinal cord becomes injured in front of these nerves imme- 

 diate death is the result. The other part of this bunch of 

 nerves supply the shoulder, chest, and muscles of the front 

 legs. Passing backwards along the spinal cord is found the 

 sympathetic system of nerves, which go to supply the 

 bowels, stomach, liver, kidneys, and other organs situated 

 in the abdominal cavity. Continuing backwards along the 



