Gemelli and obturator internus muscles: different heads of one muscle?
BACKGROUND
The superior gemellus, inferior gemellus, and obturator internus muscles were once regarded as a single muscle judging from their insertion and function. However, current textbooks of anatomy do not treat them as one muscle. In gross anatomy, the classification of muscles depends largely upon the nerve supply, so that the present author re-examined the nerve supply to the three muscles.


METHODS
Fourteen nerve-muscle specimens were taken from 12 cadavers (five males and seven females) and examined with the unaided eye and under a dissecting microscope.


RESULTS
(1) The modes of nerve supply to the superior gemellus, inferior gemellus, and obturator internus muscles differed; however, the nerves to the muscles shared the same spinal nerve components. (2) The gemelli formed a muscular pocket ("gemellus pocket") through which obturator internus muscle passed.


CONCLUSIONS
In light of this knowledge on nerve muscle relationships, the difference in the pattern of nerve supply to the superior gemellus, inferior gemellus, and obturator internus muscles cannot be the basis for stating that the muscle are independent. Rather, their fusion to form the gemellus pocket and their common insertion suggest that they are different heads of one muscle.
Shinohara
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Division of Human Sciences, Faculty of Medicine, Toyama Medical and Pharmaceutical University, Japan.
D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000294:innervation*; D010388:Pelvis