ANATOMY OF THE AUDITORY ORGAN OF THE BLACK FINLESS PORPOISE, NEOPHOCAENA PHOCANOIDES

1.The S-shaped external auditory meatus begins from a minute orifice on the side of the head and terminates at the tympanic membrane,with its passage,though very narrow,not blocked.After passing blubber the meatus becomes enclosed by auricular cartilages with which four auricular muscles are associated,namely,museulus auricularis inferior,museulus auricularis posterior,musoulus auricularis occipi-talis and intrinsic ear muscle.2.The apertura tympanic is divided into two parts:superior and inferior.The tympanic membrane located at inferior apertura tympanic is very thick.The malleus does not directly contact with malleus by tympanic ligament.3.All three auditory ossicles are small bones stout and short in form.The pro-cessus gracilis of malleus fuses with tympanic bone by synosteosis,While the head of malleus forms with ledge of periatie bone into a joint Basis stapes connect with oval window through connective tissues,thus it is easy to separate.4.As seen in land mammals,the two middle ear muscles,museulus tensar tympani and museulus stapedius,are well developed.5.There are five air sacs belonging to middle ear:anterior sac,pterygaia sac,medial sac and posterior sac.Among them the anterior sac is the biggest one.The sacs are filled with trabeculae.6.The tympano-periotic bone is as hard as the enamel cloisonne of tooth.There is no synosteosis between this bone and cranium,and by means of connective tissues it connects with the surrounding bones.7.There are one and a half spiral cochlea turns.The three ductus semicircularis are not uniform in length.Among them the canalis semicircularis posterior is the longest,the canalis semicircularis lateralis the shortest.