AUDITORY ORGAN. 



201 



in them of an organ of Corti in the cochlea. A tympanic mem- 

 brane is present in most Reptiles (with the exception of Ophidia, 

 Hatteria, and Chamaeleo) and in all Birds. The osseo-cartilaginous 

 columella is well developed, and varies much in the different 

 forms. 



FIG. 165. MEMBRANOUS LABYRINTH OF THE PIGEON. (After C. Hasse.) 



S, sacculns ; pb, pars basilaris ; mr, membrane of Reissner ; lag, lagena ; SB, FB, 

 HB, anterior and posterior vertical, and horizontal canals; SA, FA, HA, 

 ampullae of the anterior and posterior vertical, and horizontal canals. 



FIG. 166. MEMBRANOUS LABYRINTH OF Ox. (After C. Hasse.) 



S, saccnlus ; Ee.ut, recessus utriculi ; VB, blind sac at the origin of the cochlea ; Cr, 

 canalis reuniens ; pb, pars basilaris ; lag, lagena ; SB, FB, HB, anterior and 

 posterior vertical, and horizontal canals ; SA, FA, HA, the ampullae of these 

 canals ; Co, canal commissure ; N, auditory nerve. 



Mammals. The Monotr ernes appear to form a connecting 

 link between the Reptilia, or, more correctly perhaps, the post- 



