Nummela S, Reuter T, Hemilä S, Holmberg P, Paukku P
University of Helsinki, Department of Ecology and Systematics, Finland.
Hear Res. 1999 Jul;133(1-2):61-70. doi: 10.1016/s0378-5955(99)00053-2.
The paper first reviews our present understanding of the functional morphology of the odontocete (toothed whale) ear. The tympano-periotic complex forming the ear region consists of a ventral bowl-shaped tympanic bone in direct contact with the surrounding soft tissues and the incident sound, and a dorsal periotic bone containing the inner ear. Apparently sound brings the tympanic bone, and especially its thin tympanic plate, into vibration. The ossicles in the air-filled middle ear cavity form a bridge from the tympanic plate to the periotic bone connecting the vibrating plate to the oval window and the inner ear. Our computer tomography (CT) sections and camera lucida drawings reveal two hitherto unknown features of the odontocete ear, both of them of potential relevance to sound reception and impedance matching. (1) It is well known that, in addition to the ossicular chain, two other bone structures connect the tympanic to the periotic bone. We show that the most delicate parts of these extra-ossicular connections consist of thin and folded bony sheets which apparently allow compliance in the tympano-periotic bone contacts and enable plate vibration in relation to the periotic bone. (2) The round head of the malleus, in combination with a fitting round depression on the periotic side, seems to form a joint. We propose that this (hypothetical) joint, together with the adjacent structures, forms a lever producing an amplification of the vibration velocity at the level of the oval window.
本文首先回顾了我们目前对齿鲸（有齿鲸）耳朵功能形态的理解。构成耳部区域的鼓室-围耳骨复合体由与周围软组织和入射声音直接接触的腹侧碗状鼓膜骨，以及包含内耳的背侧围耳骨组成。显然，声音使鼓膜骨，尤其是其薄的鼓膜板发生振动。充满空气的中耳腔内的听小骨形成了一座从鼓膜板到围耳骨的桥梁，将振动的鼓膜板连接到椭圆窗和内耳。我们的计算机断层扫描（CT）切片和明视野绘图揭示了齿鲸耳朵两个迄今未知的特征，这两个特征都可能与声音接收和阻抗匹配有关。（1）众所周知，除了听骨链外，还有另外两个骨骼结构将鼓膜与围耳骨相连。我们发现，这些听骨外连接中最精细的部分由薄而折叠的骨片组成，这些骨片显然允许鼓室-围耳骨接触具有顺应性，并使鼓膜板相对于围耳骨振动。（2）锤骨的圆头与围耳骨一侧的适配圆形凹陷相结合，似乎形成了一个关节。我们提出，这个（假设的）关节与相邻结构一起形成了一个杠杆，在椭圆窗水平上产生振动速度的放大。
