Claes Raf, Muyshondt Pieter G G, Van Hoorebeke Luc, Dhaene Jelle, Dirckx Joris J J, Aerts Peter
Laboratory of Functional Morphology, University of Antwerp, Antwerp, Belgium.
Department of Mechanical Engineering, Vrije Universiteit Brussel, Brussels, Belgium.
J Anat. 2017 Mar;230(3):414-423. doi: 10.1111/joa.12566. Epub 2016 Nov 29.
The avian middle ear differs from that of mammalians and contains a tympanic membrane, one ossicle (bony columella and cartilaginous extra-columella), some ligaments and one muscle. The rim of the eardrum (closing the middle ear cavity) is connected to the neurocranium and, by means of a broad ligament, to the otic process of the quadrate. Due to the limited number of components in the avian middle ear, the possibilities of attenuating the conduction of sound seem to be limited to activity of the stapedius muscle. We investigate to what extent craniokinesis may impact the components of the middle ear because of the connection of the eardrum to the movable quadrate. The quadrate is a part of the beak suspension and plays an important role in craniokinesis. Micro-computed tomography was used to visualize morphology and the effect of craniokinesis on the middle ear in the domestic chicken (Gallus gallus domesticus). Both hens and roosters are considered because of their difference in vocalization capacity. It is hypothesized that effects, if present, of craniokinesis on the middle ear will be greater in roosters because of their louder vocalization. Maximal lower jaw depression was comparable for hens and roosters (respectively 34.1 ± 2.6° and 32.7 ± 2.5°). There is no overlap in ranges of maximal upper jaw elevation between the sexes (respectively 12.7 ± 2.5° and 18.5 ± 3.8°). Frontal rotation about the transversal quadrato-squamosal, and inward rotation about the squamosal-mandibular axes of the quadrate were both considered to be greater in roosters (respectively 15.4 ± 2.8° and 11.1 ± 2.5°). These quadrate rotations did not affect the columellar position or orientation. In hens, an influence of the quadrate movements on the shape of the eardrum could not be detected either; however, craniokinesis caused slight stretching of the eardrum towards the caudal rim of the otic process of the quadrate. In roosters, an inward displacement of the conical tip of the tympanic membrane of 0.378 ± 0.21 mm, as a result of craniokinesis, was observed. This is linked to a flattening and slackening of the eardrum. These changes most likely go along with a deformation of the extra-columella. Generally, in birds, larger beak opening is related to the intensity of vocalization. The coupling between larger maximal upper jaw lifting in roosters and the slackening of the eardrum suggest the presence of a passive sound attenuation mechanism during self-vocalization.
鸟类的中耳与哺乳动物的不同，它包含一个鼓膜、一块听小骨（骨性耳柱骨和软骨性外耳柱骨）、一些韧带和一块肌肉。鼓膜边缘（封闭中耳腔）与脑颅相连，并通过一条宽韧带与方骨的耳突相连。由于鸟类中耳的组成部分数量有限，减弱声音传导的可能性似乎仅限于镫骨肌的活动。我们研究了颅骨运动在多大程度上可能会因为鼓膜与可活动的方骨相连而影响中耳的组成部分。方骨是喙悬韧带的一部分，在颅骨运动中起重要作用。利用微型计算机断层扫描技术来观察家鸡（原鸡）中耳的形态以及颅骨运动对其的影响。由于母鸡和公鸡在发声能力上存在差异，所以对两者都进行了研究。据推测，由于公鸡叫声更大，颅骨运动对其中耳产生的影响（如果存在的话）会更大。母鸡和公鸡的最大下颌下压角度相当（分别为34.1±2.6°和32.7±2.5°）。两性之间最大上颌上抬角度范围没有重叠（分别为12.7±2.5°和18.5±3.8°）。公鸡围绕横向方骨 - 鳞骨以及围绕方骨的鳞骨 - 下颌轴的向内旋转都被认为更大（分别为15.4±2.8°和11.1±2.5°）。这些方骨旋转并未影响耳柱骨的位置或方向。在母鸡中，也未检测到方骨运动对鼓膜形状的影响；然而，颅骨运动导致鼓膜向方骨耳突的尾缘轻微拉伸。在公鸡中，观察到由于颅骨运动，鼓膜圆锥尖端向内移位0.378±0.21毫米。这与鼓膜的变平和松弛有关。这些变化很可能伴随着外耳柱骨的变形。一般来说，在鸟类中，较大的喙张开幅度与发声强度相关。公鸡较大的最大上颌上抬幅度与鼓膜松弛之间的关联表明，在自我发声过程中存在一种被动声音衰减机制。
