Fritzsche Franziska, Maier Wolfgang, Ruf Irina
Institut für Ökologie, Evolution und Diversität, Goethe-Universität Frankfurt am Main, Frankfurt am Main, Germany.
Abteilung Messelforschung und Mammalogie, Senckenberg Forschungsinstitut und Naturmuseum Frankfurt, Frankfurt am Main, Germany.
Anat Rec (Hoboken). 2024 Aug 28. doi: 10.1002/ar.25565.
The three mammalian auditory ossicles enhance sound transmission from the tympanic membrane to the inner ear. The anterior anchoring of the malleus is one of the key characters for functional classification of the auditory ossicles. Previous studies revealed a medial outgrowth of the mallear anterior process, the processus internus praearticularis, which serves as an anchor for the auditory ossicle chain but has been often missed due to its delicate nature. Here we describe the development and morphology of the malleus and its processus internus praearticularis in the cricetine rodent Mesocricetus auratus, compared to selected muroid species (Cricetus cricetus, Peromyscus maniculatus, and Mus musculus). Early postnatal stages of Mesocricetus show the formation of the malleus by fusion of the prearticular and mallear main body. The processus internus praearticularis forms an increasing broad lamina fused anteriorly to the ectotympanic in adult stages of all studied species. Peromyscus and Mus show a distinct orbicular apophysis that increases inertia of the malleus and therefore these species represent the microtype of auditory ossicles. In contrast, the center of mass of the malleus in the studied Cricetinae is close to the anatomical axis of rotation and their auditory ossicles represent the transitional type. The microtype belongs to the grundplan of Muroidea and is plesiomorphic for Cricetidae, whereas the transitional type evolved several times within Muroidea and represents an apomorphic feature of Cricetinae.
三种哺乳动物的听小骨增强了声音从鼓膜到内耳的传递。锤骨的前固定是听小骨功能分类的关键特征之一。先前的研究揭示了锤骨前突的内侧突出部分，即关节前内侧突，它作为听小骨链的固定点，但由于其结构精细，常常被忽略。在这里，我们描述了金黄地鼠（Mesocricetus auratus）中锤骨及其关节前内侧突的发育和形态，并与选定的鼠科物种（欧洲仓鼠Cricetus cricetus、鹿鼠Peromyscus maniculatus和小家鼠Mus musculus）进行了比较。金黄地鼠出生后的早期阶段显示，关节前骨和锤骨主体融合形成锤骨。在所有研究物种的成年阶段，关节前内侧突形成一个越来越宽的薄片，向前与鼓室外壁融合。鹿鼠和小家鼠显示出明显的环形突，增加了锤骨的惯性，因此这些物种代表了听小骨的微型类型。相比之下，所研究的仓鼠亚科中锤骨的质心接近解剖学旋转轴，它们的听小骨代表过渡类型。微型类型属于鼠科的基本模式，是仓鼠科的原始特征，而过渡类型在鼠科中多次进化，代表了仓鼠亚科的衍生特征。
