Rare case of myloglossus in Japanese cadaver: anatomical and developmental considerations

The styloglossus is one of the three extrinsic muscles of the tongue; it enters the tongue from behind. During human dissection practice for dental students at the Showa University School of Dentistry in 2006, the authors observed anomalous muscle arising from the inner surface of the mandibular angle and inserting into the tongue bilaterally. This muscle was termed myloglossus by Wood. On the right side, the myloglossus was accompanied by a weak rudimentary styloglossus, but the styloglossus was absent on the left side. The hypoglossal nerve innervated the myloglossus bilaterally, and a small branch of mandibular nerve also entered the muscle on the left side. The styloglossus develops from the styloid process and the mandibular angle as a bicipital muscle, but the segment attached to the mandibular angle generally atrophies during development. The present anomalous muscle was thought to represent persistence of this muscle bundle arising from the inner surface of the mandibular angle. The innervation of the innermost part of the left myloglossus by the mandibular nerve was explained by persistence of a vestigial nerve supplying a small muscle bundle originating from the tensor veli palatini, which had fused to the myloglossus.