Here, you will find anatomy for the triceps coxae, which consists of the obturator internus, gemellus superior, and gemellus inferior.
These three muscles were originally grouped as a single muscle. Like the triceps brachii, they have a common insertion and function. Later, they were separated because of different origins and innervation. According to one study, the innervation of these muscles is quite variable.

Triceps Coxae
The name “triceps coxae” refers to the muscular structure created by the obturator internus, gemellus superior, and gemellus inferior muscles.
Origin
- os coxae
Insertion
- Superior, posterior greater trochanter
Function
- external rotation of the hip
- abduction of the hip when flexed
- stabilize the hip

Obturator Internus
Origin
- internal lip of the obturator foramen
- internal, anteromedial aspect of the obturator membrane
Insertion
- superior, posterior greater trochanter
Function
- external rotation of the hip
- abduction of the hip when flexed
- stabilze the hip
Innervation
- obturator internus (L5,S1)

Gemellus Superior
Origin
- spine of the ischium
Insertion
- blends with the tendon of obturator internus on the superior, posterior greater trochanter
Function
- acts to assist and stabilize the obturator internus
- external rotation of the hip
- abduction of the hip when flexed
- stabilze the hip
Innervation
- obturator internus (L5,S1,S2)
Anomalies, Etc.
There are a few common anomalies in the studies that I reviewed. First, the origin may attach more superiorly to the ischium than the ischial spine. Second, there are mentions of an occasional second belly of the muscle. There are other studies of single cases with anomalies like an absence of both gemelli.

Gemellus Inferior
Origin
- ischial tuberosity
Insertion
- blends with the tendon of obturator internus on the superior, posterior greater trochanter
Function
- acts to assist and stabilize the obturator internus
- external rotation of the hip
- abduction of the hip when flexed
- stabilze the hip
Innervation
- quadratus femoris nerve (L4,L5,S1)
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