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Muscle index

The abdomen Insertion: The fibres (striated muscle) are inserted into the central
All the muscles of the anterior abdominal wall serve to protect the vis- tendon.
cera by their contraction, to produce movement and to increase the Actions: The diaphragm is involved in respiration. When the muscle
intra-abdominal pressure, as in defecation, coughing, parturition, etc. fibres contract, the diaphragm is lowered, thus increasing the vertical
All these muscles are supplied by the lower six thoracic and the first dimension of the thorax. In the later stages of contraction, using the
lumbar nerves. liver as a fulcrum it raises the lower ribs, thus increasing the width of
• External oblique the lower thorax. At the same time, it increases the intra-abdominal
Origin: From the outer surfaces of the lower eight ribs to the iliac crest pressure and is thus used in expulsive effortsadefecation, micturition,
as far forward as the anterior superior spine. parturition, etc.
Insertion: The free lower border forms the inguinal ligament between Nerve supply: Phrenic nerve (C3, 4 and 5).
the anterior superior iliac spine and the pubic tubercle. The muscle • Quadratus lumborum
becomes aponeurotic and reaches the midline where it interdigitates Origin: From the posterior part of the iliac crest.
with the opposite side to form the linea alba. The superficial inguinal Insertion: To the 12th rib.
ring is a gap in the aponeurosis above and medial to the pubic tubercle. Action: Side flexion of the trunk.
The aponeurosis contributes to the anterior rectus sheath. Nerve supply: Adjacent lumbar nerves.
Actions: Flexion of the spine, side flexion and rotation of the trunkathe • Psoas major: see lower limb (p. 165).
right external oblique produces rotation to the left.
• Internal oblique The upper limb
Origin: From the thoracolumbar fascia, the iliac crest and the lateral • Latissimus dorsi
half of the inguinal ligament. Origin: From the spines of the lower six thoracic vertebrae, the lumbar
Insertion: Into an aponeurosis which is attached to the costal margin spines via the thoracolumbar fascia and the medial part of the iliac
and to the linea aspera, after splitting to enclose the rectus abdominis, crest.
thus contributing to the rectus sheath. The lower fibres from the Insertion: To the floor of the intertubercular sulcus, curving round teres
inguinal ligament contribute to the conjoint tendon which is attached to major.
the pubic crest and the pectineal line. Actions: Adduction and medial rotation of the arm. Can hold up the
Actions: Flexion of the spine, side flexion and rotation of the trunkathe lower limb girdle as in crutch walking.
right internal oblique produces rotation to the right. Nerve supply: Thoracodorsal nerve.
• Transversus abdominis • Serratus anterior
Origin: From the thoracolumbar fascia, the iliac crest and the lateral Origin: From the lateral surfaces of the upper eight ribs.
one third of the inguinal ligament. Also from the inner surfaces of the Insertion: Into the medial border of the scapula.
lower six ribs, interdigitating with the diaphragm. Actions: Protraction of the scapula and rotation so that the glenoid
Insertion: The aponeurosis passes to the linea aspera, contributing to points upwards, thus helping in abduction of the upper limb. Helps to
the rectus sheath. The lower fibres help to form the conjoint tendon. keep the scapula in contact with the chest wall.
Actions: Most of the fibres are transverse and thus pull in and flatten the Nerve supply: Long thoracic nerve.
abdominal wall. • Levator scapulae
• Rectus abdominis Origin: From the transverse processes of the upper cervical vertebrae.
Origin: From the anterior surfaces of the 5th, 6th and 7th costal Insertion: To the medial border of the scapula above the spine.
cartilages. Action: Elevates the scapula.
Insertion: The pubic crest and tubercle and the front of the symphysis. Nerve supply: C3 and 4.
There are three tendinous intersections in the upper part of the muscle • The rhomboids
which are adherent to the anterior rectus sheath. Origin: From spines of thoracic vertebrae.
Actions: The muscle is enclosed in the rectus sheath. A strong flexor of Insertion: To the medial border of the scapula.
the trunk, it can also tilt the pelvis backwards. In a person lying prone, Action: Bracing back the scapula.
rectus contracts when the head is lifted from the pillow or when the leg Nerve supply: Dorsal scapular nerve.
is raised from the bed. • Trapezius: See p. 167.
For further important details of the muscles of the anterior abdom- • Pectoralis major
inal wall, see the inguinal canal and the rectus sheath (p. 30). Origin: From the sternum and the upper six costal cartilages and from
• The diaphragm the medial half of the clavicle.
Origin: From the inner surfaces of the lower six ribs, from the back of Insertion: To the lateral lip of the intertubercular sulcus.
the xiphisternum, from the right and left crura which are attached, Actions: Adduction, flexion and medial rotation of the arm.
respectively, to the upper three and the upper two lumbar vertebrae, and Nerve supply: Medial and lateral pectoral nerves.
from the medial and lateral arcuate ligaments which bridge over the • Pectoralis minor
psoas major and quadratus lumborum. Origin: From the 3rd, 4th and 5th ribs.
162 Muscle index