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ANATOMY OF THE NKBVOUS SYSTEM. 



The nervous system is divided into two minor systems, the 

 cerebrospinal, which is to a considerable extent influenced by 

 the win of the animal, and the sympathetic, which is not directly 

 influenced by the will. 



In the first the center is made up of two portions, the brain and 

 the spinal cord. 



The brain is situated in the cranial cavity; the other, the spinal 

 cord, is elongated and continuous with the braip and is situated 

 in the canal of the vertebral column. 



The communicating portion of this system consists of the cere- 

 bro-spinal nerves, which leave the brain and spinal cord in sym- 

 metrical pairs, and are distributed to the voluntary muscles, to 

 the organs of common sensation, and to those of special sense. 



The sympathetic system consists of a chain of ganglia (small 

 brains) connected by a nerve cord. They extend from the head 

 to the coccyx along either side of the spine; the nerves of this 

 system are distributed to the involuntary muscles, mucous mem- 

 branes, internal organs, and blood vessels. 



A nerve consists of a bundle of tubular fibers held together by 

 dense connective tissue. 



The nerve fibers represent and form a conducting apparatus. 



ANATOMY OF THE EYE. 



The eye is the organ of sight and is situated in the orbital 

 fossa. It is spherical in shape and filled with fluid. The front 

 portion, called the cornea, is clear as glass, admitting the light 

 to the back part of the eye, where it strikes the retina, an expan- 

 sion of the optic nerve which transmits impressions to the brain. 

 The colored . portion, or iris, acts as a curtain, regulating the 

 amount of light admitted, the center of the iris being known as 

 the pupil. The crystalline lens is a small transparent body sit- 

 uated immediately behind the pupil; it is thick in the center and 

 tapers toward the edges. Its function is to draw the rays of 

 light to a focus and refract them on the retina. When the lens 

 is diseased and no light can pass through it the animal is said to 

 have a cataract. The eyelids are two movable curtains, superior 

 and inferior, which protect the eye. 



