In adults, the intermediate tendon of digastricus muscle usually runs along the medial or lateral side of the stylohyoideus muscle insertion. To provide a better understanding of the variations, we examined the topographical anatomy of the muscle and tendon in fetuses. We examined histological sections from six early-term, 26 mid-term and six near-term fetuses (approximately 8–9, 12–18 weeks and 25–33 weeks). At early-term, an initial sheath of intermediate tendon of digastricus muscle received the stylohyoideus muscle at the superior aspect. The muscle and tendon was distant from the hyoid. At mid-term, near the insertion to the hyoid greater horn, the stylohyoideus muscle consistently surrounded more than 2/3 of the intermediate tendon circumference. In contrast, we found no near-term specimen in which the stylohyoideus muscle surrounded the intermediate tendon. The multilayered tendon sheath was fully developed until near-term and connected to the body of hyoid by an intermuscular septum between the thyrohyoideus muscle and one or two of suprahyoid muscles. Therefore, the hyoid insertion of the styloglossus muscle was a transient morphology at mid-term. The stylohyoideus muscle insertion was appeared to move from the tendon sheath to the hyoid greater horn and, until near-term, return to the tendon sheath. A fascia connecting the tendon sheath to the body of hyoid was strengthened by the suprahyoid and infrahyoid muscles. The latter muscles seemed to regulate fixation/relaxation of the intermediate tendon to the hyoid. The stylohyoideus muscle slips sandwiching the intermediate tendon might be a rare morphology.

中文翻译：

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不断生长的茎舌骨肌插入舌骨，特别参考其与二腹肌中间肌腱的地形关系：利用人类胎儿的组织学研究

在成人中，二腹肌的中间肌腱通常沿着茎突舌骨肌止点的内侧或外侧延伸。为了更好地理解这些变化，我们检查了胎儿肌肉和肌腱的地形解剖结构。我们检查了 6 个早期胎儿、26 个中期胎儿和 6 个近期胎儿（大约 8-9、12-18 周和 25-33 周）的组织学切片。在早期，二腹肌中间肌腱的初始鞘在上部接受茎突舌骨肌。肌肉和肌腱远离舌骨。在中期，靠近舌骨大角插入处，茎舌骨肌始终包围超过 2/3 的中间肌腱周长。相比之下，我们没有发现近期标本中茎舌骨肌包围中间肌腱。多层腱鞘直到近足月才完全发育，并通过甲状舌骨肌和一两块舌骨上肌之间的肌间隔膜连接到舌骨体。因此，茎舌肌的舌骨插入是中期的短暂形态。茎舌骨肌插入似乎从腱鞘移动到舌骨大角，并且直到近期返回到腱鞘。连接腱鞘和舌骨体的筋膜由舌骨上肌和舌骨下肌强化。后者的肌肉似乎调节中间肌腱对舌骨的固定/松弛。夹着中间肌腱的茎舌肌滑移可能是一种罕见的形态。