366 THE MUSCULAR SYSTEM. 
the iliac crest between the muscles of the back and abdominal wall. It is formed 
by the union of three fascial strata, called respectively the vertebral aponeurosis or 
RECTUS ABDOMINIS 
l= 
OBLIQUUS EXTERNUS 
OBLIQUUS INTERNUS 
TRANSVERSALIS 
ABDOMINIS» 
Fascia transversalis 
Peritoneum A 
4 
/ 
as 
Duodenum 
: +—Psoas fascia 
Bxtraperitoneal 
Kidney 
Second lumbar 
vertebra 
Psoas 
Lumbar fascia 
lumbar faseia 
LATISSIMUS DORSI 
MULTIFIDUS 
SPINA 
QUADRATUS LUMBORUM » SaOE ETS 
“DORSIL 
Middie layer of lumbar fascia 
ILIO-COSTALIS 
LONGISSIMUS DORSI 
Anterior layer of 
posterior layer, just 
described; the 
middle and _ the 
anterior layers, 
The middle layer 
is a fascia which 
stretches outwards 
from the ends of 
the transverse pro- 
cesses of the 
lumbar  vertebree, 
between the erec- 
tor spine behind 
and the quadratus 
lumborum muscle 
in front! / “ihe 
anterior layer is 
attached to the 
lumbar vertebree 
at the junction of 
their transverse 
processes and 
bodies. It covers 
the front of the 
quadratus lum- 
Vertebral aponeurosis 
borum muscle, and 
separates it from 
the psoas. At the 
outer borders of the quadratus lumborum and erector spine muscles the three 
layers are blended together to form the lumbar fascia, which in turn gives partial 
origin to the obliquus internus and transversalis abdominis muscles. 
Fic. 269.—TRANSVERSE SECTION THROUGH THE ABDOMEN, OPPOSITE THE 
SEcOND LUMBAR VERTEBRA, 
THE MUSCLES OF THE BACK. 
The muscles of the back are arranged in four series according to their attach- 
ments: (1) vertebro-scapular and vertebro- humeral, (2) vertebro - costal, (3) 
vertebro-cranial, and (4) vertebral. They are in irregular strata, the most 
superficial muscles having the most widely separated attachments. 
The first series of muscles of the back, connecting the axial skeleton to the 
upper limb, have already been described. They are arranged in two layers: 
(1) trapezius and latissimus dorsi, superficially ; (2) levator anguli scapulee, and 
rhomboidei beneath the trapezius. 
The remaining muscles are almost entirely axial, and may be divided into four 
groups: (1) serrati postici, superior and inferior, and splenius capitis and colli ; 
(2) erector spinee and complexus; (3) transverso-spinales (semispinalis and multi- 
fidus spinee); and (4) the small deep muscles (rotatores, interspinales, intertrans- 
versales, and suboccipital muscles). 
First Group. 
The serratus posticus superior has a membranous origin from the ligamentum 
nuchz and the spines of the last cervical and upper three or four thoracic vertebre. 
It is directed obliquely downwards and outwards, to be inserted by separate slips 
into the second, third, fourth, and fifth ribs. The muscle is concealed by the 
vertebro-scapular muscles, and crosses obliquely the splenius, erector spine, and 
complexus. It lies superficial to the vertebral aponeurosis. 
The serratus posticus inferior has a membranous origin through the medium 
