SEC. IV 



ANATOMY OF BIRDS 



^ 



cylinder encloses a section of the cerebro-spinal axis, or principal 

 nervous system of a vertebrate (brain and spinal cord, v\rhence arise 



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all the nerves of the body, excepting those of the sympathetic 

 nervous system). The lower ring is the hcBmal arch (Gr. atfj^a, haima, 



