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i FASCLE AND MUSCLES OF PERINEUM AND PELVIS. 405 
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Hesselbach’s triangle, bounded by the line of Poupart’s ligament below, by the 
rectus muscle internally, and by the deep epigastric artery on the mesial side of 
the internal abdominal ring externally, is the site of one form of inguinal hernia. 
The spermatic cord passes over the base of the triangle, covered over by the 
aponeurosis of the obliquus externus. Behind the cord are the fascia transversalis 
and the conjoint tendon, which may be said to form the floor of the triangle. 
The posterior muscles of the abdominal wall and false pelvis include the 
psoas (magnus and parvus) and iliacus, described already (p. 343), and the quadratus 
jumborum. 
The quadratus lumborum lies on the posterior wall of the abdomen external 
to the psoas, and extends between the iliac crest and the last rib. It arises from 
the posterior part of the iliac crest, from the ilio-lumbar ligament, and from the 
transverse processes of the lower lumbar vertebrae. It is inserted above into the 
lower border of the last rib and the transverse processes of the upper lumbar 
vertebre. It is enclosed between the anterior and middle layers of the lumbar 
aponeurosis (p. 365), and is placed behind the colon, kidney, and psoas muscle, in 
front of the multifidus spinee and the lumbar transverse processes. 
NERVE SUPPLY. 
The nerve supply of all the foregoing muscles except the psoas, cremaster, quadratus 
lumborum, and iliacus, is derived from the anterior primary divisions of the lower six thoracic 
nerves. The pyramidalis muscle is innervated by the last thoracic nerve. The cremaster muscle 
receives its supply from the genito-crural nerve, whilst the quadratus lumborum is innervated 
by the first three or four lumbar nerves. The psoas and iliacus muscles are supplied, directly or 
through the anterior crural nerve, from the second, third, and fourth lumbar nerves. 
ACTIONS. 
Many of the actions of the above muscles have already been given in previous sections. (1) 
Their chief action is to retract the abdominal walls, and, by compressing the contents of the 
abdomen, they are powerful agents in vomiting, defecation, micturition, parturition, and 
laboured expiration. (2) They are also flexors of the spine and pelvis—the muscles of both sides 
acting together ; the spine and pelvis are laterally flexed, when one set of muscles acts alone. 
(3) The quadratus lumborum is a muscle of inspiration, an extensor of the spine, and a lateral 
flexor of the spine and pelvis. 
FASCIA AND MUSCLES OF THE PERINEUM AND PELVIS. 
FASCLH OF THE PERINEUM. 
The superficial fascia of the perineum possesses certain special features. It 
is continuous with the superficial fascia of the abdominal wall, thigh, and buttock, 
and is prolonged on to the penis and scrotum. In relation to the penis, it is 
devoid of fat and consists only of areolar tissue. In relation to the scrotum, it is 
intermingled with involuntary muscular fibres, and constitutes the dartos muscle, 
which assists in suspending the testicles and corrugating the skin of the scrotum. 
This fascia also forms a septum for the scrotum, extending upwards and incompletely 
separating the two testicles and their coverings. In the female the superficial 
fascia takes a large share in the formation of the mons veneris and labia majora, in 
which a considerable quantity of fat occurs. 
The fascia over the posterior part of the perineum tills up the ischio-rectal fossz, 
in the form of two pads of adipose tissue, on either side of the rectum and anus. 
Over the tuberosities of the ischium the fat is largely replaced by bands of fibrous 
tissue closely adherent to the subjacent deep fascia. 
The fascia in the anterior part of the perinewm closely resembles the same 
fascia in the groin. It is divisible into a superficial fatty and a deeper membranous 
layer ; the former continuous with the same layer in the thigh, and with the fat 
of the ischio-rectal fossa posteriorly. The deeper membranous layer is attached 
laterally to the pubic arch, posteriorly to the base of the triangular ligament, and 
in the middle line to the root of the penis (bulb and corpus spongiosum) by a 
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