下オトガイ棘；オトガイ舌骨筋棘 - Spina mentalis inferior; Spina geni inferior
On the internal surface of body of mandible, near the lower part of the symphysis is a pair of laterally placed spines, termed the superior mental spine (superior genial spine), which give origin to the Genioglossi.
Immediately below these is a second pair of spines, the inferior mental spine (inferior genial spine) or more frequently a median ridge or impression, for the origin of the Geniohyoidei.
In some cases the mental spines are fused to form a single eminence, in others they are absent and their position is indicated merely by an irregularity of the surface.
This definition incorporates text from a public domain edition of Gray's Anatomy (20th U.S. edition of Gray's Anatomy of the Human Body, published in 1918 – from http://www.bartleby.com/107/).
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