Download D24-1 UNIT 24. DISSECTION: ANTERIOR ABDOMINAL WALL

UNIT 24.
DISSECTION: ANTERIOR ABDOMINAL WALL
STRUCTURES TO IDENTIFY:
Linea alba
Superficial epigastric artery
External oblique
Transverse abdominis
Rectus sheath
Superior epigastric artery
Deep circumflex iliac artery
Deep inguinal ring
Medial crural fibers
Intercrural fibers
Pectineal ligament
Spermatic cord
Iliohypogastric nerve
Ductus (vas) deferens
Pampiniform venous plexus
Superficial circumflex iliac artery
Internal oblique
Rectus abdominis
Transversalis fascia
Inferior epigastric artery
Superficial inguinal ring
inguinal ligament
Round ligament
Ilioinguinal nerve
Scrotum
Testes
Epididymus
Testicular vessels
DISSECTION INSTRUCTIONS:
1. First incision: A mid-line incision 3 mm deep from the xiphoid process to the
symphysis pubis, circling the umbilicus.
Second incision: An incision 1 cm below the inguinal ligament from the mid-line to
the gluteal region where the skin was removed from the back. Reflect the skin from
the abdomen.
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2. Locate and clean the superficial epigastric and the superficial circumflex iliac vessels
(N. plates 255, 256; G. plates 2.4, 2.5). Carefully make a mid-line incision through
the superficial fascia following the first skin incision. Do not cut through the linea
alba. Make a second incision through the superficial fascia from the umbilicus to the
crest of the ilium. While reflecting the superficial fascia laterally from the midline,
look for anterior cutaneous nerves and perforating vessels piercing the anterior
lamella of the rectus sheath and entering the superficial fascia (N. plate 255, 257; G.
plates 2.4, 2.5).
3. Clean the external oblique m. (N. plates 249, 254 255; G. plates 2.3, 2.5, 2.6, 2.7), but
do not destroy the superficial inguinal ring. Detach the external oblique muscle from
its origin on the ribs and separate the muscle from the internal oblique (N. plate 254;
G. plate 2.5B,2.6, 2.8, 2.9). The inguinal ligament and the superficial inguinal ring
must be kept intact, so make an incision through the external oblique muscle from
just above the crest of the ilium to two inches above the pubic symphysis. Do not try
to separate the aponeurosis of the external oblique from the internal oblique at the
linea semilunaris. Compare the direction of muscle fibers in the internal and external
oblique muscles. Note the direction of the most inferior internal oblique muscle
fibers compared with its superior fibers. Carefully incise the internal oblique muscle
in the midaxillary line and its attachments to the costal margin and iliac crest; reflect
it forward to expose the transverse abdominis muscle. Between these muscles will be
the main trunks of the intercostal nerves (N. plate 257; G. plates 2.4, 2.5B). Attempt
to identify the deep circumflex iliac artery.
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4. Open the rectus sheath (N. plates 250, 251, 255 - 257; G. plates 2.4, 2.5); make a
longitudinal incision through its exposed anterior portion, from a point just below the
xiphoid process to a pint just above the pubic symphysis, parallel and just lateral to
the linea alba. From the upper end of the first incision, make a transverse incision
and then a second transverse incision just below the umbilicus. Now make a
transverse incision in the rectus abdominis m. just below the umbilicus and reflect the
muscle superiorly. Identify the superior and inferior epigastric arteries (N. plate 255;
G. plate 2.5). The posterior lamella of the rectus sheath can now be seen. It consists
of the aponeurosis of the transverse abdominis and the internal oblique. The posterior
lamella ends below the level of the umbilicus as the arcuate line; below this level you
only have transversalis fascia (N. plates 251, 255, 256; G. plate 2.59). Below the
arcuate line the anterior lamella of the rectus sheath consists of the aponuerosis of all
three muscles. Just above the pubic symphysis the internal oblique and the transverse
abdominis fuse to form the conjoined tendon.
5. Locate the superficial inguinal ring in the external oblique aponeurosis just above the
pubic tubercle (N. plates 260, 261; G. plates 2.7, 2.8). The collagen bundles forming
the superior and medial boundaries of the ring are the medial crural fibers and the
inferior fibers are the lateral crural fibers. Lateral to the superficial ring, youhave the
intercrural fibers. Identify the spermtic cord, the round ligament and the ilioinguinal
nerve, all emerge from the superficial inguinal ring.
6. Make a small incision through the linea alba below the umbilicus to reach the
peritoneal cavity. Pull the abdominal wall away from the abdominal contents so as
not to cut them. Extend the incision through the body wall transversely from one
ASIS to the other. Inspect the deep surface of the anterior abdominal wall below the
incision (N. plates 252, 253; G. plate 2.17). Extending from the apex of the bladder
to the umbilicus is a peritoneal fold containing the median umbilical ligament, which
is the remnant of the fetal urachus (N. plate 253; G. plate 2.17). Another peritoneal
fold appears to come out of the pelvis lateral to the bladder and ascends to the
umbilicus. This fold is called the median umbilical fold and it contains the medial
umbilical ligament, the obliterated umbilical artery. Further lateral is another fold
containing the inferior epigastric vessels. This peritoneal fold is called the lateral
umbilical fold (N. plate 253; G. plate 2.17). The deep inguinal ring is just lateral to
the lateral umbilical fold. Remove the peritoneum form about a two-inch radius
around the deep inguinal ring and clean the structures which enter or leave the ring.
In the male, these are the ductus deferens and the neurovascular bundle for the testes;
in the female it is the round ligament of the uterus (N. plates 255, 259, 387; G. plate
2.8 – 2.10, 2.15).
7. Remove the skin from the anterior surface of the pubis and follow the spermatic cord
down to the testes (N. plates 255, 259, 387; G. plate 2.8, 2.12, 2.15). Identify tunica
albuginea, tunica vaginalis, epididymus, ductus deferens and the pampiniform venous
plexus.
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