鸭的中耳及传声器官

THE SOUND-CONDUCTING APPARATUS IN THE MIDDLE-EAR OF DOMESTIC FOWLS AND THE GENERAL STRUCTURE OF THE TYMPANIC CAVITY

1.鸭的中耳传声器官主要包括:鼓膜、听骨、张肌及韧带四部分。结构比较简单。它所以能完成传声过程中一系列的复杂动作,主要靠每一组成部分的特殊结构和各部使之间的连接。2.鼓膜北京鸭的鼓膜直径约6毫米,构成外耳道内端的背侧壁。鼓膜面自后,外,上方向前、内、下方倾斜。柱状听骨的外端附着在鼓膜的后内下区,占全鼓膜面的1/4—1/3。听骨中脚前端附着部约位于鼓膜中央。该部又为鼓膜外张肌的附着部。3.鼓膜外张肌鼓膜外张肌自枕骨项面的枕骨大孔下部两侧起始。肌腹成半环形,前端腱纤维混入鼓膜的听骨附着区。张肌收缩时,向外开张鼓膜,以调整膜的紧张度。4.鸭的听骨采取斜位,在传声过程中有三个优点 (1)当张肌收缩或弛缓时,听骨可借本身斜度的改变,在保持听骨两端位置不变的情况下,来调整鼓膜与前庭窗之间的距离,保持内耳的压力不发生大的变化;(2)鼓膜振动时可以借听骨斜度的改变,使内耳的压力发生变化;(3)前庭窗可以免受听骨垂直向的正面冲击,特别是在声音有较大的突然变化时,由于力的方向改变,在一定程度上可以保证内耳不致遭受破坏。5.家禽鼓膜外张肌的名称问题鸭与鸡以及一般鸟类的鼓膜张肌,根据它所在位置和力的作用方向,应称之为鼓膜外张肌。相当哺乳动物鼓膜张肌,在鸟类可称之为鼓膜内张肌。在家禽由于鼓膜向外隆凸的关系,已失掉对鼓膜张力的调整作用,因此退化为腱质。

1)The sound-conducting apparatus in the middle-ear of domestic fowls includes the membrana tympani,columella,musculus tensor tympani and several ligaments.These or- gans possess a simpler structure than in mammals,and yet their peculiar structures and interconnections between them make it possible to accomplish the conduction of sound waves. 2)The membrana tympani is about 6mm in diameter and forms the dorso- medial wall of the medial end of the external acoustic meatus.The surface of the mem- brane slopes ventro-medially,with the lateral end of the columella attached to its caudo- medial region.The tendon of the tensor muscle is inserted on its lateral surface and pushes its central part outward,producing a concavity of its inner surface. 3)The tensor muscle arises from the ventro-lateral part of the foramen magnum of the occipital bone and ends in a delicate tendon inserting on the lateral surface of the drum membrane where the extracolumella is attached.When the muscle contracts,it draws the drum outward and tenses the membrane,therefore it is better named as tensor tympani externum. 4)The columella,with its shaft directing in an oblique direction,has two special functional characteristics:(a)When the tensor tympani retracts the membrane,the columella changes its oblique angle to compensate the variation in the distance between the drum and the fenestra vestibuli;(b)The oblique position of the columella diminishes the force of the sound waves(push and pull)and avoids damaging the drum membrane. 5)The inner surface of the membrane tympani is concave,and therefrom the ten- sor tympani internum has lost its functional significance to regulate the tension of the drum,and has degenerated into a ligament.This ligament is divided into medial and lateral parts;the medial part is stronger then the lateral. 6)The ligaments of membrana tympani are the drum-tubal and marginal.Liga- ments of the columella are the columello-squamosal and ligament proprium.The columello-squamosal ligament is the most important apparatus to fix the columella,and the crucial point between the columella and ligament is the hinge of the columella move- ment.