THE ARMY HORSE. 



41 



The brain is situated in the cranial cavity; the spinal cord 

 is elongated and continuous with the brain and is situated in 

 the canal of tlie vertebral cobinm. 



The connnunicating- portion of this system consists of the 

 cerebro-spinal nerves, which leave the brain and spinal cord in 

 synnnetrical pairs, and are distributed to the voluntary nuis- 

 cles, to the organs of common sensation, and to those of special 

 sense. 



The sympathetic system consists of a double chain of ganglia 

 (small brains), extending from the head to the coccyx, along 

 either side of the spine, and connected by nerve cords. The 

 ffanirlia are also connected to branches of the cerebro-spinal 

 nerves, thus uniting the two systems. The nerves of the sym- 

 pathetic system are distributed to the involuntary muscles, 

 mucous membranes, internal organs, and blood vessels. 



ANATOMY or THE EYE. 



(Pi;it(. vni.) 



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

 cavity. It is spherical in shape and is filled with fluid. The 

 front portion, called the cornea^ is perfectly clear and admits 



PLATE VIII. 



Section of the eye. 

 c, ConieH; e, eyelids; t\ lluiil; i, ins; I, cr.vstalliiie U-ii.--; c, uptic iicrvi-; ;>, pupil; r. n-tiiiii. 



the liglit to the l)ack part of the eye. where it strikes the retina, 

 an expansion of the optic ncr>'c: through this nerve impres- 

 sions are conveyed to the biain. Tiu- colored i)ortion or ?>/.?, 

 situated behind the cornea, acts as a curtain, regulating the 



