Obturator externus muscle
Encyclopedia
The obturator externus muscle (OE) is a flat, triangular muscle, which covers the outer surface of the anterior wall of the pelvis
.
It is sometimes considered part of the medial compartment of thigh
, and sometimes considered part of the gluteal region.
, viz., from the rami of the pubis, and the inferior ramus of the ischium; it also arises from the medial two-thirds of the outer surface of the obturator membrane
, and from the tendinous arch which completes the canal for the passage of the obturator vessels and nerves.
The fibers springing from the pubic arch extend on to the inner surface of the bone, where they obtain a narrow origin between the margin of the foramen and the attachment of the obturator membrane.
The fibers converge and pass posterolateral and upward, and end in a tendon which runs across the back of the neck of the femur and lower part of the capsule of the hip joint and is inserted into the trochanteric fossa of the femur.
by piercing it.
muscle is found between the adductor brevis
and minimus
. While this muscle, when present, is similar to its neighbouring adductors, it is formed by separation from the superficial layer of the obturator externus, and is thus not ontogentically
related to the adductor muscles of the hip
. This muscle originates from the upper part of the inferior ramus of the pubis
from where it runs downwards and laterally. In half of cases, it inserts into the anterior surface of the insertion aponeurosis
of the adductor minimus. In the remaining cases, it is either inserted into the upper part of the pectineal line
or the posterior part of the lesser trochanter
.
It has been demonstrated by the course of the posterior branch of obturator nerve
that the obturator externus is divided into a superior fasciculus
and a main belly. The supernumerary muscle described above originates from the superior fasciculus, while an anomalous fasciculus — also derived from the obturator externus — originates from the main belly. The "original" obturator externus, i.e. without these supernumerary muscular parts, actually occurs in only 20% of cases, and apparently the obturator externus readily undergoes ontogenetic
variations.
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
.
It is sometimes considered part of the medial compartment of thigh
Medial compartment of thigh
The medial fascial compartment of thigh contains the hip adductors.The obturator nerve is the primary nerve supplying this compartment.The muscles in the compartment are:* gracilis* adductors** adductor longus** adductor brevis** adductor magnus...
, and sometimes considered part of the gluteal region.
Origin and insertion
It arises from the margin of bone immediately around the medial side of the obturator foramenObturator foramen
The obturator foramen is the hole created by the ischium and pubis bones of the pelvis through which nerves and muscles pass.- General structure :...
, viz., from the rami of the pubis, and the inferior ramus of the ischium; it also arises from the medial two-thirds of the outer surface of the obturator membrane
Obturator membrane
The obturator membrane is a thin fibrous sheet, which almost completely closes the obturator foramen.Its fibers are arranged in interlacing bundles mainly transverse in direction; the uppermost bundle is attached to the obturator tubercles and completes the obturator canal for the passage of the...
, and from the tendinous arch which completes the canal for the passage of the obturator vessels and nerves.
The fibers springing from the pubic arch extend on to the inner surface of the bone, where they obtain a narrow origin between the margin of the foramen and the attachment of the obturator membrane.
The fibers converge and pass posterolateral and upward, and end in a tendon which runs across the back of the neck of the femur and lower part of the capsule of the hip joint and is inserted into the trochanteric fossa of the femur.
Relations
The obturator vessels lie between the muscle and the obturator membrane; the anterior branch of the obturator nerve reaches the thigh by passing in front of the muscle, and the posterior branchPosterior branch of obturator nerve
The posterior branch of the obturator nerve pierces the anterior part of the Obturator externus, and supplies this muscle; it then passes behind the Adductor brevis on the front of the Adductor magnus, where it divides into numerous muscular branches which are distributed to the Adductor magnus and...
by piercing it.
Variation
In 33% of people a supernumerarySupernumerary body part
Supernumerary body parts are most commonly a congenital disorder involving the growth of an additional part of the body and a deviation from the body plan. Body parts may be easily visible or hidden away, such as internal organs....
muscle is found between the adductor brevis
Adductor brevis muscle
The adductor brevis is a muscle in the thigh situated immediately behind the pectineus and adductor longus.-Origin and insertion:It is somewhat triangular in form, and arises by a narrow origin from the outer surfaces of the superior and inferior rami of the pubis, between the gracilis and...
and minimus
Adductor minimus muscle
In human anatomy, the adductor minimus is a small and flat skeletal muscle in the thigh which constitutes the upper, lateral part of the adductor magnus muscle....
. While this muscle, when present, is similar to its neighbouring adductors, it is formed by separation from the superficial layer of the obturator externus, and is thus not ontogentically
Ontogeny
Ontogeny is the origin and the development of an organism – for example: from the fertilized egg to mature form. It covers in essence, the study of an organism's lifespan...
related to the adductor muscles of the hip
Adductor muscles of the hip
In human anatomy, the adductor muscles of the hip is a group of muscles of the thigh.-Muscles:The adductor group is made up of:*Adductor brevis*Adductor longus*Adductor magnus*Adductor minimus This is often considered to be a part of adductor magnus....
. This muscle originates from the upper part of the inferior ramus of the pubis
Inferior pubic ramus
The inferior pubic ramus is a part of the pelvis and is thin and flat. It passes laterally and downward from the medial end of the superior ramus; it becomes narrower as it descends and joins with the inferior ramus of the ischium below the obturator foramen....
from where it runs downwards and laterally. In half of cases, it inserts into the anterior surface of the insertion aponeurosis
Aponeurosis
Aponeuroses are layers of flat broad tendons. They have a shiny, whitish-silvery color, are histologically similar to tendons, and are very sparingly supplied with blood vessels and nerves. When dissected, aponeuroses are papery, and peel off by sections...
of the adductor minimus. In the remaining cases, it is either inserted into the upper part of the pectineal line
Pectineal line (pubis)
The pecten pubis or pectineal line of the pubis is a ridge on the superior ramus of the pubic bone.The pecten pubis forms part of the pelvic brim.Lying across it are fibers of the pectineal ligament and the proximal origin of the pectineus muscle....
or the posterior part of the lesser trochanter
Lesser trochanter
The lesser trochanter of the femur is a conical eminence, which varies in size in different subjects-Anatomy:It projects from the lower and back part of the base of the femur neck.From its apex three well-marked borders extend:...
.
It has been demonstrated by the course of the posterior branch of obturator nerve
Posterior branch of obturator nerve
The posterior branch of the obturator nerve pierces the anterior part of the Obturator externus, and supplies this muscle; it then passes behind the Adductor brevis on the front of the Adductor magnus, where it divides into numerous muscular branches which are distributed to the Adductor magnus and...
that the obturator externus is divided into a superior fasciculus
Muscle fascicle
In anatomy, a fascicle is a bundle of skeletal muscle fibers surrounded by perimysium, a type of connective tissue.Specialized muscle fibers in the heart that transmit electrical impulses from the Atrioventricular Node to the Purkinje Fibers are fascicles, also referred to as bundle branches...
and a main belly. The supernumerary muscle described above originates from the superior fasciculus, while an anomalous fasciculus — also derived from the obturator externus — originates from the main belly. The "original" obturator externus, i.e. without these supernumerary muscular parts, actually occurs in only 20% of cases, and apparently the obturator externus readily undergoes ontogenetic
Ontogeny
Ontogeny is the origin and the development of an organism – for example: from the fertilized egg to mature form. It covers in essence, the study of an organism's lifespan...
variations.