62 ANTHROPOLOGY. 
lunar form, and in the median line; one for the inferior vena cava (foramen . 
ven cave or quadrilaterum), nearly square, and to the right side; and one 
for the cesophagus (hiatus esophageus), elliptical, and to the left side. 
- The quadratus lumborum is a thick, flat, irregularly. square muscle, 
situated in the lumbar region next the spine, forming part of the posterior 
wall.of the abdomen. It arises from the posterior fourth of the crest of the 
ilium and from the ilio-lumbar ligament; it is inserted into the extremity 
_of the transverse processes of the four first lumbar vertebrae and. of the 
last dorsal. Its use is to bend the spine to one side, to depress the last 
rib, and thus assist in expiration; both muscles acting together support the 
spine. 
Psoas parvus, a long, thin, and narrow muscle, is situated behind the 
psoas magnus and arises from the lower edge of the side of the body of the 
last dorsal vertebra, also from the body of the first lumbar, and the inter- 
vertebral substance; it ends in a thin tendon which crosses the psoas 
magnus and is inserted into the ilio-pectineal eminence and adjacent part 
of the brim of the pelvis. Use: to assist in bending forwards the body or 
in raising the pelvis. 
Psoas magnus extends along the sides of the lumbar vertebrz, the brim 
of the pelvis, and the anterior and inner part of the thigh, as a long, round, 
and fleshy muscle. It arises by two planes of fasciculi, the one anterior 
from the sides of the border of the two last dorsal and four first lumbar 
vertebree; the other posterior, from the bases of the transverse processes. 
The fibres become attached to a tendon in common with those of the 
iliacus muscle, which passing around the hip joint becomes inserted into 
and around the lesser trochanter of the femur. Its use is to flex the thigh 
on the pelvis, or the pelvis on the thigh; in standing it supports the 
spine and prevents its bending backwards; it is especially concerned in 
walking. 
The iliacus internus, a flat, radiated, or triangular muscle, arises from the 
transverse process of the last lumbar vertebra, ilio-lumbar ligament, base 
of the sacrum, inner margin of the crest of the iliim, the brim of the ace- 
tabulum, &c., and is inserted into the common tendon of the psoas magnus 
as already described. It assists the psoas in flexing and rotating the 
thigh. 
We next proceed to the consideration of the perineal muscles, the first 
of which is the sphincter ani externus, a flat, thin, oval muscle, open in the 
middle. It arises from a fibro-cellular substance extending from the os 
coceygis to the rectum (recto-coccygeal ligament), and encircling the anal 
orifice, is inserted into the raphe or prominent hard ridge of the perineum 
and into the superficial fascia. It serves to close and raise the anus, also 
to draw the bulb of the urethra downwards and backwards, and to com- 
press it. 
The sphincter ani internus vel orbicularis is a thick fasciculus of mus- 
cular fibres, encircling the lower extremity of the rectum, with no attach- 
ment to the rectum behind, and only a slight one to the central point 
before, but is in close contact with the mucous membrane of the intestine. 
768 
