Structure and Motion Laboratory, Department of Veterinary Basic Sciences, The Royal Veterinary College, University of London, Hatfield, Hertfordshire, UK.
J Anat. 2010 Apr;216(4):423-45. doi: 10.1111/j.1469-7580.2009.01202.x. Epub 2010 Feb 10.
Crocodylians exhibit a fascinating diversity of terrestrial gaits and limb motions that remain poorly described and are of great importance to understanding their natural history and evolution. Their musculoskeletal anatomy is pivotal to this diversity and yet only qualitative studies of muscle-tendon unit anatomy exist. The relative masses and internal architecture (fascicle lengths and physiological cross-sectional areas) of muscles of the pectoral and pelvic limbs of American alligators (Alligator mississippiensis Daudin 1801) were recorded for an ontogenetic series of wild specimens (n = 15, body masses from 0.5 to 60 kg). The data were analysed by reduced major axis regression to determine scaling relationships with body mass. Physiological cross-sectional areas and therefore muscle force-generating capacity were found to be greater in the extensor (anti-gravity) muscles of the pelvic limb than in the pectoral limb, reflecting how crocodylians differ from mammals in having greater loading of the hindlimbs than the forelimbs. Muscle masses and architecture were generally found to scale isometrically with body mass, suggesting an ontogenetic decrease in terrestrial athleticism. This concurs with the findings of previous studies showing ontogenetic decreases in limb bone length and the general scaling principle of a decline of strength : weight ratios with increasing size in animals. Exceptions to isometric scaling found included positive allometry in fascicle length for extensor musculature of both limbs, suggesting an ontogenetic increase in working range interpreted as increasing postural variability - in particular the major hip extensors - the interpretation of which is complicated by previous described ontogenetic increase of moment arms for these muscles.
鳄类表现出多种多样的陆地步态和肢体运动，这些步态和运动仍未得到充分描述，对了解它们的自然历史和进化具有重要意义。它们的肌肉骨骼解剖结构对这种多样性至关重要，但目前仅存在肌肉-肌腱单元解剖结构的定性研究。本研究记录了美洲鳄（Alligator mississippiensis Daudin 1801）野生幼体（n = 15，体重 0.5 至 60 千克）的胸鳍和腹鳍的相对质量和内部结构（肌节长度和生理横截面积）。通过降维主轴回归分析确定与体重的比例关系。结果发现，与胸鳍相比，腹鳍的伸肌（抗重力肌）的生理横截面积更大，因此产生的肌肉力量更大，这反映了鳄类与哺乳动物的不同之处在于后肢承受的负荷大于前肢。肌肉质量和结构通常与体重等比例缩放，表明陆地运动能力在个体发育过程中逐渐降低。这与先前的研究结果一致，这些研究表明，在个体发育过程中，四肢骨骼长度减小，以及随着动物体型增大，力量与体重的比值下降的一般缩放原则。等比例缩放的例外情况包括四肢伸肌肌节长度的正异速生长，这表明工作范围的个体发育增加，解释为姿势变异性增加——特别是主要的髋关节伸肌——但由于这些肌肉的力臂在个体发育过程中增加，因此解释较为复杂。
