538 



AMPHIBIA. 



The medulla oblongata, on the roof of which the pia 

 mater forms a very vascular "choroid plexus." 



In the tadpole the pineal body lies outside the skull 

 under the skin of the head ; it atrophies at the metamor- 

 phosis, so that in the adult the stalk only is represented. 



FIG. 180. Nervous system of Frog. (After ECKER.) 



i-io. The cranial nerves ; oc, eyes ; crb, in front of optic chiasma ; 

 to, optic tract ; sym, sympathetic system : msp, spinal cord ; 

 sp, spinal nerves. 



The cranial nerves are, as usual, on each side the follow- 

 ing : 



(1) Olfactory, from the olfactory lobe to the nose ; 



(2) Optic, crossing and interlacing with its fellow ; 



(3) Oculomotor, to four muscles of the eye ; 



