Markey Molly J, Marshall Charles R
Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, USA.
J Morphol. 2007 Jan;268(1):89-102. doi: 10.1002/jmor.10504.
The aim of this study is to connect specific sutural morphologies with the specific types of deformation they experience. To meet this goal, we quantified the morphologies of the interfrontal (IF), interparietal (IP), and frontoparietal (FP) sutures in the extant fish Polypterus endlicherii, and used our published measurements of in vivo deformation of these sutures during feeding to infer how suture morphology and function are connected. Specifically, we found that three relatively simple measures of cross-sectional suture complexity (i.e., the ratio of total sutural length to its shortest end-to-end length; amount of sutural overlap; and size of the largest interdigitation) can be used to distinguish between the IF, FP, and IP sutures, which exhibit very different cross-sectional shapes and responses to loading. Interestingly, these differences in cross-sectional morphology are not reflected by the linear traces of these sutures on the surface of the skull, implying that cross-sectional shape of a suture must be known to infer the loading conditions it experiences. Plotting the three cross-sectional metrics against one another to yield a sutural morphospace shows that the IF, IP, and FP sutures define regions that are largely distinct from one another. Our previous measurements of strain across these sutures suggested that the FP region would lie between the IF and IP regions; instead, the FP region is largely set apart from the other two fields. Based on this discovery, and on the locations of cranial muscles, we propose a new model of deformation in the skull of P. endlicherii during feeding, in which rotation parallel to the skull roof is combined with bending, subjecting the FP suture to complex shearing. Finally, although the sutures of P. endlicherii appear to be significantly less complex than those of mammals, these fish sutures show a similar range of morphologies and perform similar functions as do mammalian sutures.
本研究的目的是将特定的缝合形态与它们所经历的特定变形类型联系起来。为实现这一目标，我们对现存鱼类恩氏多鳍鱼的额间（IF）、顶间（IP）和额顶（FP）缝合处的形态进行了量化，并利用我们之前发表的这些缝合处在进食过程中的体内变形测量数据，来推断缝合形态与功能之间的联系。具体而言，我们发现可以使用三种相对简单的横截面缝合复杂度量度（即缝合总长度与其最短端到端长度的比值、缝合重叠量以及最大交错指状突的大小）来区分IF、FP和IP缝合处，它们呈现出非常不同的横截面形状和对负载的响应。有趣的是，这些横截面形态上的差异并未在颅骨表面这些缝合处的线性痕迹中体现出来，这意味着必须了解缝合处的横截面形状才能推断其经历的负载条件。将这三个横截面指标相互绘制以生成一个缝合形态空间，结果表明IF、IP和FP缝合处定义的区域在很大程度上彼此不同。我们之前对这些缝合处应变的测量表明，FP区域应位于IF和IP区域之间；相反，FP区域在很大程度上与其他两个区域分开。基于这一发现以及颅肌的位置，我们提出了一个恩氏多鳍鱼在进食时颅骨变形的新模型，其中平行于颅顶的旋转与弯曲相结合，使FP缝合处承受复杂的剪切力。最后，尽管恩氏多鳍鱼的缝合处似乎比哺乳动物的缝合处明显简单，但这些鱼类的缝合处显示出与哺乳动物缝合处相似的形态范围并执行相似的功能。
