XII 



PHYLUM CHORDATA 



477 



form ot a biconvex lens. Sclerotic plates are present and 

 there is a large pecten in the form of a plaited and strongly 

 pigmented membrane projecting into the cavity of the eye 

 from the entrance of the optic nerve. 



V 



O.I 



FIG. 272. Columba livia. The brain ; A, from above ; B, from below: C, from 

 the left side. cb. cereballum ; c. h. cerebral hemispheres ; f. flocculus : inf. in- 

 fundibulum ; m. o. medulla oblongata ; o. I. optic lobes ; o. t. optic tracts ; f.n. 

 pineal body ; II XII, cerebral nerves ; j/./, first spinal nerve. (From Parker's 

 Zootouiy.) 



The auditory organ is chiefly distinguished from that of 

 Reptiles by the great development of the cochlea. The 

 tympanic cavity and columella have the same arrangement 



