Department of Medical Anatomical Sciences, Western University of Health Sciences, Pomona, CA, USA.
Department of Anthropology, University of Florida, Gainesville, FL, USA.
Anat Rec (Hoboken). 2021 Apr;304(4):832-844. doi: 10.1002/ar.24514. Epub 2020 Oct 13.
Ectotympanic bone morphology is commonly used as a large-scale phylogenetic indicator across primates. Less well-understood is the intraspecies variation in this characteristic and the dynamic ways in which it affects and is affected by overall basicranial shape. This study attempts to clarify relationships between the external ear canal and basicranial shape among humans in a sample of archaeological human crania. The ectotympanic length and orientation were hypothesized to correlate with the shape of the cranial base and particularly with shape variables associated with relative brachycephaly. Basicranial shape in 80 computed tomography (CT) scans of adult humans were quantified using landmark coordinate data, with particular emphasis on the cranial base and auditory structures. Scaled ectotympanic lengths were taken from interlandmark distances and then compared to shape variation of the whole basicranium as summarized by procrustes shape variables and principal components analysis (PCA). The length of the ectotympanic bone was correlated with total cranial base variation. Long ectotympanic bones were found to be associated with brachycephalic individuals and less flexed basicrania. Additionally, long ectotympanic bones were found to be more horizontally oriented, as opposed to inferiorly sloped. We suggest that as brachycephaly increases the distance between the otic capsule and the pinna, the ectotympanic bone lengthens in response.
鼓室外骨形态通常被用作灵长类动物的大规模系统发育指标。但人们对该特征的种内变异以及它对整体颅基形状的影响和受其影响的动态方式了解甚少。本研究试图在考古人类颅骨样本中阐明人类中耳道与颅基形状之间的关系。假设鼓室外骨的长度和方向与颅底形状相关，特别是与相对短头型相关的形状变量相关。使用 landmark 坐标数据对 80 例成人 CT 扫描的颅基形状进行了定量分析，特别强调了颅底和听觉结构。从 landmark 之间的距离中获取鼓室外骨的缩放长度，然后将其与通过主成分分析（PCA）总结的整个颅基的形状变化进行比较。鼓室外骨的长度与总颅基变异相关。长的鼓室外骨与短头型个体和较低弯曲的颅底有关。此外，长的鼓室外骨更倾向于水平定向，而不是向下倾斜。我们认为，随着短头型的增加，耳囊和耳郭之间的距离增加，鼓室外骨会相应地变长。
