The brain is the center of the whole nervous system, and is situated in the cranial cavity, surrounded by three delicate membranes, the outer one being attached to the inner wall of the bones forming the brain cavity. The brain contains several important nerves called cranial nerves, which are given off from the brain and pass down through the various foramen or openings in the head to supply the different organs 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 olfactory 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 pharynx or gullet, giving it the power of swallowing. The spinal cord passes from the brain through the openings in the bones of the back, which gives off numerous small nerves that supply the muscles of the back with motion and feeling. Nearly opposite the shoulder blade the spinal cord gives off a large trunk of nerves, portion 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 immediate death is the result. The other portions of this trunk of nerves supply the shoulder, chest and muscles of the front legs. Passing backward 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. Coming backwards along the spinal cord to about opposite the hip bones, is another set of nerves, one of which goes to supply the rectum, or back bowels. Others go to the generative and urinary organs where they assist in performing their functions. Other nerves pass to the small organs situated in the pelvic cavity; some of these nerves pass down to the hind legs, supplying them with nervous power. The remainder of the nerves go to supply the tail. The difference between the nervous system of a horse and other animals is not worth mentioning. CHAPTER VII. AESTHESIOLOGY. The study of organs of special sense, the ear, eye and organs of special sensation, skin, hair, foot, etc. THE EAR. The apparatus of hearing is composed of three parts the outer, middle, and inner ear; the two first being accessory for the collection and transmission of sounds, and the latter the essential organ which receives the impressions thus conveyed.