MORPHOLOGY OF HIGHER TYPES 



141 



of a moderately large mass of nervous tissue, the brain, located in the 

 head, and a spinal cord, dorsal to the alimentary tract, extending back- 



cer 



Lopt 



Fig. 111. — Nervous system of the frog, showing cranial and spinal nerves and sym- 

 pathetic system, ventral view. I-X, cranial nerves; cer, cerebrum; L opt, optic lobe; n, 

 Jiasal sac: s, sympathetic system; spc, spinal cord. {After Wiedersheim.) 



ward from the brain almost to the end of the trunk. From the brain 

 arise 12 pairs (10 in lower vertebrates) of cranial nerves which extend to 



