THE FROG S BEAIN 



387 



The frog's brain. — The brain may be divided into three 

 parts, called respectively, the forebrain, midbrain, and hind- 

 brain. From these parts of the brain are given off ten 

 pairs of nerves called cranial nerves. These nerves are 

 made up of fibers called nerve fibers. Those cranial nerves 

 whose fibers bring impulses or messages to the brain are 

 called afferent or sensory nerves. Those whose fibers con- 



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Pig. 179 — Frog brain; /, top view; ^, olfactory nerves; .8, olfactory lobes; C, Z>. 

 forebrain; E, midbrain; -F, optic lobes; G, bindbrain; H^ medulla; /, cord; J^ 

 K, L, M, N, nerves; //, ventral view; ///, lateral view. 



vey impulses from the brain are called efferent or motor 

 nerves. Several of these nerves contain both efferent and 

 afferent fibers, and such are called mixed nerves. 



