SECTION VI. THE NERVOUS SYSTEM AND 

 SENSE ORGANS 



Anatomically, the nervous system is divided into three sub- 

 systems: 1, the peripheral system, a network of nerves 

 conveying impulses from the sense organs, and to the 

 muscles and glands; 2, the cerebro-spinal (central) system, 

 a central co-ordinating tube; and 3, the autonomic (sym- 

 pathetic) system supplying the viscera and associated with 

 the peripheral system. The sense organs are the nose, eyes, 

 and ears, together with scattered sensory elements in the 

 skin and mouth. 



Place the frog on the dissecting board, ventral side up, 

 and carefully remove the urogenital system, taking care 

 not to injure the dorsal aorta. Note that the kidneys are 

 retro-peritoneal, and therefore outside of the codome. 

 Identify the following structures. 



151. The periganglionic glands (calciferous bodies), 



are silvery white lymph glands surrounding the 

 ganglia of the ten pairs of spinal nerves, which 

 leave the vertebral column between the vertebrae. 



152. The first spinal (hypoglossal) nerve is a very small 

 nerve, leaving the spinal cord between the first and 

 second vertebrae, and running cephalad and ventrad 

 to the tongue. One or two fibres bend caudad to join 



153. the second spinal (brachial) nerve, which is very 

 large, and leaves the vertebral column between the 

 second and third vertebrae and runs to the arm. It 

 is joined by 



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