CHAPTER 5 
ABDOMEN AND PELVIS 
5.1 LIMITS AND LANDMARKS 
The abdominal cavity {cavum abdominis) is the 
largest serous sac in the body of the hamster, ex- 
tending horn the diaphragm to the pelvic inlet 
{apertura pelvis cranialis), or brim of the pelvis. Its 
greatest expansion is represented by a line from the 
diaphragmatic insertions on the sternum to the 
cranial margin of the pubic symphysis (symphysis 
pubica). The cranial boundary is formed by the dia- 
phragm, describing a dome-like arch over the cav- 
ity, which protrudes high into the bony thorax up 
to the level of the seventh thoracic vertebra (Figs. 
3-11,5-1, 5-2). 
The dorsal wall is supported by the lumbar ver- 
tebrae {vertebrae lumbales) (Figs. 2-1, 3-1). The 
dorsal wall includes the psoas major, iliacus and 
quadratus lumborum muscles. The lateral wall 
consists of the obliquus internus, and the ventral 
wall the rectus abdominis musculature. The lateral 
surface is supported cranially by the last rib and 
cartilages and caudally by the iliac crest (crista 
iliaca), and the ventral surface cranially by the end 
of the sternal body and the xiphoid process (Figs. 
5-1, 5-2). 
As in man, the abdominal cavity is separate from 
the pelvic cavity (cavum pelvis). The bony support 
of the pelvis dorsally is provided by the sacral verte- 
brae (vertebrae sacrales) and by the first caudal 
vertebrae (vertebrae caudales). The lateral bound- 
ary is formed by the ilium (os ilium) and the ischium 
(os ischium). The pubic bone (os pubis) and the is- 
chium confer skeletal support ventrally. The pelvic 
inlet is obliquely situated and is described by a 
plane passing through the sacral prominence (pro- 
montorium) of the sacral base (basis ossis sacri) and 
the cranial rim of the symphysis. The cross-section 
of the pelvic inlet is heart-shaped, while that of the 
pelvic outlet (apertura pelvis caudalis) is oval. 
5.2 BONY SKELETON OF THE 
ABDOMEN AND PELVIS 
The lumbar-sacral column forms a spinal kypho- 
sis (Figs. 3-1, 5-2). The six lumbar vertebrae roof 
the abdominal cavity, extending for a length of 
52 mm. The vertebral bodies are relatively long, 
and kidney-shaped in transverse section (Fig. 5-3). 
The vertebral canal (canalis vertebralis) is dorso- 
ventrally compressed. The spinous processes are 
long, rectangular, and of moderate height, with 
thickened dorsal borders. The last lumbar vertebra 
(Fig. 5-4) is the most prominent, with a spinous 
process 6.9 mm long and 5.1 high. 
The sacrum (os sacrum) consists of usually three 
synostosed vertebrae measuring 21.3 mm in length 
(Fig. 5-5). The transverse processes of all three ver- 
tebrae form a continuous surface (pars lateralis), 
the cranial portion of which is expanded into an 
ear-shaped shallow concavity (facies auricularis) 
for articulation with the ilium (Figs. 3-1, 5-6). 
The sacral canal (canalis sacralis) is completely en- 
closed. 
There are 17 caudal vertebrae (vertebrae cau- 
dales) disposed in a lordosis (Fig. 3-1). They de- 
crease caudally in both length (from 5.8 mm to 
1.3 mm) and complexity. The first four or five 
caudal vertebrae retain articular processes and 
transverse processes, but caudal to this, the verte- 
brae are simple pentagonal spools. 
The pelvic bone (os coxae) ossifies from three 
separate centers: os ilium, os ichii, and os pubis. 
The sutures are obliterated by 12 months postpar- 
tum (Table 23), and a single adult structure 41 mm 
long and 16 mm wide remains (Fig. 5-7). The 
ilium is a long rod-like structure that diverges 
craniolaterally (Fig. 5-6). It constitutes a portion 
of the acetabulum. The craniomedial surface is 
roughened (facies auricularis) for articulation with 
the sacrum. The ischium constitutes the caudo- 
dorsal and caudal portions of the pelvis, while the 
pubis constitutes the ventral portion of the posterior 
pelvis. The pubes join across the ventral midline to 
form the pubic symphysis (symphysis pubica). The 
pubis and ischium surround the large triangular 
obturator opening (foramen obturatum). The ace- 
tabulum, the articular surface for the head of the 
femur (Fig. 5-6), is composed of all three pelvic 
bones, and measures 5.4 mm in diameter. 
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