Metazoa Rana. 



307 



Having briefly sketched the essential features in the 

 structure of the skeleton we must now pass to the nervous 

 system, which has been already described as lying in the 

 brain-box and the canal formed by the apposition of the 

 neural arches of the vertebrae. 



The nervous system. The nervous system of the frog 

 shows a very great advance in differentiation upon that of 



FIG. 166. -BRAIN or FROG, A, FROM ABOVE ; n, FROM BELOW. (Ecker.) 



01 



HO --i- 



i, olfactory nerves ; Ol, olfactory lobes ; CH, cerebral hemispheres ; L T, 

 lamina terminalis ; Th, thalamencephalon ; PG, pineal gland; OpL, 

 optic lobes ; Ci, cerebellum ; MO, medulla oblongata ; 2, optic nerves ; 

 OT, optic chiasma ; H, pituitary body ; 3-10, cerebral nerves. 



AmpMoxus. In the amphibian brain, indeed, we have 

 represented all the most important parts of the brain of the 

 mammal (dog, rabbit, &c.). The nervous system consists of 

 a spinal cord enlarged anteriorly to form the brain, the former 

 being lodged in the neural canal of the vertebral column, 

 the latter in the cavity of the skull, or cranium. From both 



x 2 



