殿筋 is read as でんきん (denkin) and means gluteus.
でんきん
denkin
だいでんきん
gluteus maximus
でんかく
palace
すじ
(Edo period) counter for hundreds of mon (obsolete unit of currency)
はらすじ
sit-up (exercise)
てっきん
reinforced concrete
あらすじ
outline
おおすじ
ひとすじ
one bloodline
しんきん
heart muscle
みちすじ
path
しょうそくすじ
informed circles
せすじ
seam down the back (of clothing)