XII 



PHYLUM CHORDATA 



423 



nan's or external nostril and the posterior naris or internal 

 nostril (Fig. 235, p. na.\ which opens into the mouth 

 immediately external to the vomer. 



The eye and the auditory organ have the usual structure, 

 but in connection with the latter there is an important 





L.ol 



-M.d) 



FIG. 239. Rana esculenta. The brain. A, from above ; B, from below. HH. 

 cerebellum ; Hyp. pituitary body ; Jnf. infundibulum ; L. ol. olfactory lobe ; 



Anatomy.') 



accessory organ of hearing not hitherto met with. Bounded 

 externally by the tympanic membrane and internally by 

 the outer wall of the auditory capsule is a considerable 



