Endo Hideki, Watanabe Kazunori, Hayashi Yoshihiro, Matsuzaki Mika, Sakai Takeo, Itoh Takuya, Koie Hiroshi, Kimura Junpei, Stafford Brian J
Department of Zoology, National Science Museum, Tokyo, Tokyo 169-0073, Japan.
Ann Anat. 2003 Jul;185(4):367-72. doi: 10.1016/S0940-9602(03)80063-8.
We examined the bone movement in the forepaw and hind paw in the aardvark (Orycteropus afer) by using three-dimensional (3D)-computed tomography (CT) techniques and osteometrical methods to confirm the functional adaptation of the extremities as a digging system. The four metacarpal bones could be strongly bent from the distal carpal bones. The distal end of the second and third metacarpal bones possessed enlarged smooth articulation surfaces that allowed the proximal phalanx to bend at a sharp angle. However, the articulation surface was not well-developed in the distal end of the fourth and fifth metacarpal bones and the proximal phalanx could bend at smaller angle in these two lateral digits. The proximal phalanges sharply crook from the metatarsal in the first, second, third and fourth digits in the hind paw. We suggest that the medial two digits in the forepaw directly contribute to the crushing, when these proximal phalanges crook in the phase of power stroke. In contrast the lateral third and fourth digits may act as sweeper of the crushed soil. These suggestions regarding the different functional adaptation between medial two digits and lateral two digits are consistent with the anatomical data of the forearm musculature. In the hind paw, we suggest that the second, third and fourth digits are functionally similar and that the hind paw may not act as a crushing apparatus but as a running motor or soil-sweeper similarly using these main three digits.
我们通过三维（3D）计算机断层扫描（CT）技术和骨测量方法，研究了土豚（Orycteropus afer）前爪和后爪的骨骼运动，以确认四肢作为挖掘系统的功能适应性。四块掌骨可以从远端腕骨处强烈弯曲。第二和第三掌骨的远端具有扩大的光滑关节面，使近端指骨能够以锐角弯曲。然而，第四和第五掌骨的远端关节面发育不完善，近端指骨在这两个外侧手指中弯曲角度较小。后爪的第一、第二、第三和第四趾的近端指骨从跖骨处急剧弯曲。我们认为，在前爪的发力阶段，当这些近端指骨弯曲时，内侧的两个手指直接参与挤压动作。相比之下，外侧的第三和第四手指可能起到清扫被压碎土壤的作用。关于内侧两个手指和外侧两个手指不同功能适应性的这些推测与前臂肌肉组织的解剖学数据一致。在后爪方面，我们认为第二、第三和第四趾在功能上相似，后爪可能不像前爪那样作为挤压工具，而是类似地利用这三个主要趾作为奔跑动力或土壤清扫器。
