Montero Ricardo, Daza Juan D, Bauer Aaron M, Abdala Virginia
Cátedra Vertebrados, Facultad de Ciencias Naturales, Universidad Nacional de Tucumán; Instituto de Herpetología, Fundación Miguel Lillo, Tucumán, Argentina.
Department of Biological Sciences, Sam Houston State University, Huntsville, Texas, 77340.
J Morphol. 2017 Oct;278(10):1400-1411. doi: 10.1002/jmor.20719. Epub 2017 Jun 20.
Sesamoids are elements that originate as intratendinous structures due to genetic and epigenetic factors. These elements have been reported frequently in vertebrates, although cranial sesamoids have been recorded almost exclusively in non-tetrapod Osteichthyes. The only tetrapod cranial sesamoids reported until now have been the transiliens cartilage (of crocodiles and turtles), and another one located in the quadrate-mandibular joint of birds. Here, we examined seven squamate species using histological sections, dissections of preserved specimens, dry skeletons, cleared and stained specimens, computed tomographies (CT), and report the presence of other cranial sesamoids. One is attached to the cephalic condyle of the quadrate, embedded in the bodenaponeurosis and jaw adductor muscles of Ophiodes intermedius (Anguidae). The other sesamoid is found at the base of the basicranium of several squamates, capping the sphenoccipital tubercle, on the lateral side of the basioccipital-basisphenoid suture. This bone has previously been reported as "element X." We reinterpret it as a basicranial sesamoid, as it is associated with tendons of the cranio-cervical muscles. This bone seems to have the function of resisting tension-compression forces generated by the muscle during flexion the head. This element was previously known in several squamates, and we confirmed its presence in three additional squamate families: Gymnophthalmidae, Gekkonidae, and Pygopodidae. The evidence suggests that cranial sesamoids are a widespread character in squamates, and it is possible that this feature has been present since the origin of the group.
籽骨是由于遗传和表观遗传因素而起源于肌腱内结构的元素。这些元素在脊椎动物中经常被报道，尽管颅骨籽骨几乎只在非四足硬骨鱼类中被记录到。到目前为止，唯一被报道的四足动物颅骨籽骨是（鳄鱼和海龟的）跨髂软骨，以及位于鸟类方骨 - 下颌关节处的另一块籽骨。在这里，我们使用组织学切片、保存标本的解剖、干燥骨骼、透明和染色标本、计算机断层扫描（CT）对七种有鳞目物种进行了检查，并报告了其他颅骨籽骨的存在。一块附着在方骨的头部髁突上，嵌入中间蛇蜥（蛇蜥科）的颈枕腱膜和咬肌中。另一块籽骨在几种有鳞目动物的颅底基部被发现，覆盖蝶枕结节，位于枕骨基部 - 蝶骨基部缝线的外侧。这块骨头以前被报道为“元素X”。我们将其重新解释为颅底籽骨，因为它与颅颈肌肉的肌腱有关。这块骨头似乎具有抵抗头部弯曲时肌肉产生的拉伸 - 压缩力的功能。这个元素以前在几种有鳞目动物中已知，我们在另外三个有鳞目科中证实了它的存在：裸眼蜥科、壁虎科和鳞脚蜥科。证据表明颅骨籽骨在有鳞目动物中是一个广泛存在的特征，并且这个特征可能自该类群起源以来就已存在。
