CHARACTERS OF VERTEBRATES. 169 



each side of the bony mass, arching over, and uniting above. 



* 



All of the vertebrae, except those in the tail, possess this chan- 

 nel or tube. 



Within the skull is a mass called the brain, and running 

 from this through a hole in the skull is a long white cord 

 called the spinal cord or cerebro-spinal cord, and this always 

 runs along on the back of the spine or vertebral column, 

 passing through the arch or hole of each vertebra just de- 

 scribed. In fact, the spinal cord is protected from injury by 

 passing through this bony tube. 



These features with various modifications will be found 

 in all animals having a vertebral column, that is, a central 

 longitudinal axis either of bone or of cartilage above which 

 runs the spinal cord. . 



The impulses of the animal to move originate in the 

 brain and, passing along the spinal cord, run off by means of 

 nerves, to animate the movements of the muscles. As a proof 

 of this, if the spinal cord be injured, the parts behind and 

 below it are rendered helpless. 



The ribs passing from the vertebrae arch below, and 

 form another and much larger cavity, in which are contained 

 the organs which contribute to the body's growth, such as 

 the lungs for breathing, the heart for propelling the blood, 

 the stomach for digesting the food, and so on. The follow- 

 ing figure represents a body vertebra to which are attached 

 a pair of ribs with the cavity above, in which is contained 

 the spinal cord or cerebro-spinal cord, and the cavity below, 

 in which are contained the lungs, heart, stomach, etc. 



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