由于此前的研究中发现硬化型约占到1 ~2[1,2],比例很低,因此本次研究未发现硬化型的可能原因之一是样本数量不足,但同时也不能排除此次研究人群样本的特殊性。此前的研究常常将气化良好(本文所述气化型)的样本与有一定气化但不完全的(本文所述混合型均属于这一类)样本一同归入“气化型”中[2,15],按照这一标准,本次研究中“气化型”的占比为88,气化比例非常高,我们需要考虑这种现象的产生是否与样本所属人群的生存环境有关。
本次研究样本的乳突小房体积的均值(见表3)为6.45cm3(变异范围0.81~16.13cm3,SD=3.44cm3),这一结果与韩国的Kim等[16]的结果接近,而与金和娟等[17]的结果有一定的差异。这种差异的来源可能是建立模型时对乳突小房的选择标准的差异。在本研究中,散见于明显的乳突小房周围的板障样窦腔均未计入体积。但同样的,我们也不能排除样本来源人群的不同可能导致了此一批与彼一批样本之间真实存在着差异。这些都需要在扩大样本的选取后做进一步的研究。
4.1 乳突小房不具有左右两侧差异及性别差异
在研究中,我们收集了共计112侧乳突小房的形态特征(类型)、分布范围(长与高)、表面积及体积的信息,我们将这些信息按照左右两侧、性别分别统计进行t检验,发现无论是整体形态特征,还是分布范围,或是定量测定的表面积、体积,此次研究的样本都不具有两侧差异或是性别差异。这一结果意味着,如果这一结果不是本文选择样本的特殊性导致的,那么在后续研究中研究者就可以不必过于考虑样本左右侧或性别的代表性,而某些特殊材料——例如以士兵为主体、男性占绝大多数的样本——也可加入对比,甚至在研究人类化石时也可以考虑进行单侧及单一性别间的对比。这大大方便了我们在研究过程中的材料选取。但是这一结果的反面则是我们也不能轻易地根据这一特征区分出男女性别。
4.2 乳突小房的体积与表面积成正相关
我们将测量所得的这112侧乳突小房的体积及表面积进行相关性分析,发现此二者是显著相关的,体积对于表面积的相关系数(r)为0.884,这种相关程度比我们此前所预期的更高。在三维复原技术发展之前,此前关于乳突小房的研究也曾计算过CT扫描所得的乳突小房的体积及由正侧位乳突小房面积所推导出的表面积之间的定量关系[5],虽然计算结果有所差异,但是相关系数大多与本次研究计算得到的相近。
4.3 乳突小房与乳突外部形态的关系
在我们得出“乳突小房在性别及左右两侧间无差异”的结论时,我们也验证了“乳突的长与高具有显著的性别差异”的结论,同时这种差异在乳突长、高与耳上颅高相比之后得到的相对值中仍然存在,p值为0.013。那么,乳突外部大小有性别差异,内部空腔却无性别差异,这样的情况推动我们进一步探究影响乳突小房的因素。
通过对乳突小房体积与乳突长度、高度相关性的分析,我们发现,乳突小房的体积与乳突的长显著相关,但与高的相关性不显著。同时,相关性分析所得的相关系数都较低,这意味着乳突的长度、高度对乳突小房体积影响较弱,仅根据乳突外部长度高度来推算其内部乳突小房的体积是很困难且不准确的。为了更好地研究乳突小房的体积与什么有关,我们还需要进一步探究在乳突长度、高度确定的情况下还有哪些因素影响乳突小房体积,而乳突小房的形态特征(在本文中具体称为乳突小房的气化类型)应当正是其中之一。
全体乳突小房样本的高度变异系数为0.30,大于长度变异系数0.27,说明乳突小房分布范围在高度上变异更大大,这也是受到气化程度影响的主要体现点,同时这种气化程度对乳突小房高度所造成的影响也导致了乳突小房高度与乳突高度的关联的微弱。我们试图寻找一种简单的定量指标可以在将来的研究中用以描述乳突小房的气化程度,而“乳突小房的高度”可能是适合的标准之一。
这样看来,乳突小房与乳突外部形态的关系可以总结为:内部空腔受限于乳突(甚至颞骨)的外部形态,例如长度、高度等,而在可允许的范围内通过气化程度的变化形成多变的内部形态。
4.4 关于本文结果的其他讨论
在本研究中,我们复原了大量的现代云南人样本的乳突小房模型,在进一步研究中可以对比我们所研究的其他样本或是文献中观测的现代人、部分古人类化石及一些现生灵长类的乳突小房形态,以期对乳突小房在时空上的形态、分布变化有所了解。
另外,我们采用了一种简单直观的表达方法表示乳突小房的分布范围,便于与乳突及头骨整体进行比较。但这种表示方法是可能存在问题的:观察面限于侧面,而与颞骨表面不完全平行,导致无法直接与乳突形态进行比较;此外,乳突小房的主要分布区域互相重叠,测得乳突小房的长与高会丢失形态的部分信息。因此,在未来的研究中我们需要选择更佳的指标来描述乳突小房的分布情况。
致谢:感谢中国科学院古脊椎动物与古人类研究所的侯叶茂和张亚盟在CT扫描、三维虚拟复原过程中的技术指导。
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3d virtual reconstruction and morphological variations of the mastoid air cells—take modern skulls from yunnan province for example
Zhang Xuan①,②
,	Wu Xiujie①
(①Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044;
②University of Chinese Academy of Sciences, Beijing 100049)
Abstract
Mastoid air cell system is the most important component in temporal bone pneumatic cavities. They reduce the weight of the temporal bone, and maintain the balance of air-pressure inside human body. In addition, mastoid air cells pneumatization was thought to be associated with otitis media. However, the morphological features of mastoid air cells inside the bone wall are still unclear. With recent development of high-resolution industry computed tomography(CT)and three-dimensional(3D)visualization computer techniques, researchers were able to study the morphological variations of mastoid air cells without destroying the specimens and reveal morphological features among the ancient humans. In this study, the morphological variations of mastoid air cells of modern human were analyzed using high-resolution industry CT and 3D virtual reconstruction. A total of 112 complete mastoids were obtained from 58 modern human skulls discovered in archeological sites in Yunnan Province. CT imagines were used for 3D virtual reconstruction to study the distribution, surface areas, volumes and other features of mastoid air cells. We found: (1) In 112 mastoids, 71% of the mastoid air cells were classified in pneumatic type, whereas only 12% were in diploetic type, and the rest were in mixed type. Mastoid air cell system of sclerotic type was not found in all samples. (2) The mean mastoid air cell volume was 6.45cm3(0.81~16.13cm3, SD=3.44cm3). The mean surface area was 41.36cm2(8.56~90.12cm2, SD=16.62cm2). (3) Mastoid air cells did not show significant difference in pneumatization, distribution, surface areas or volumes in different genders, and had the same lateral distribution on both sides of the head. These suggest that samples from either side of the head or different genders may be representative for morphological feature analysis. (4) A strong positive correlation was found between the volume and the surface area of mastoid air cell system with a coefficient of 0.884, which agrees with previous studies. (5) A weak correlation was found between the mastoid air cell volume and the length of mastoid. The pneumatization of mastoid air cells contributed more in shaping the height than in the length of mastoid air cell system. It also reduced the relation between the height of mastoid and the height of mastoid air cell system. Some of our data showed difference from previous studies, which may be caused by the population difference and temporal variation. Further studies on the contribution of different population and temporal variation to sample variation are needed.
Key words:mastoid air cellCT3D virtual reconstructionmodern skullsmorphologic variation