Prelab Images - Abdominal Wall

Prelab should consist of reading the lab manual and dissector answers and viewing the dissection video. To begin your study, you may find it useful to look over the Netter's or LWW Atlas images listed below.

Step 1. Review the bony landmarks. (Play movie)

Plate N268 or TG5-1B and TG5-1C shows the regions and quadrants used to describe the abdominal wall. Plates N248 or TG5-3, or TG5-1, and N486 or TG3-4 and TG3-4 show the iliac crest, anterior superior iliac spine, pubic tubercle, and pectin pubis (pectineal line). The pubic crest is not labeled in these drawings, but is between the pubic tubercle and pectineal line in plate N486 or TG3-4 and TG3-4. The iliopectineal line is not labeled in these plates, but is essentially the arcuate line plus the pectineal line. Plate N185 or TG4-4 reviews the rib cage and costal margins.

Step 2. Remove the skin from the anterior abdominal wall and examine its subcutaneous tissue and cutaneous nerves. (Play movie)

Remove the skin from the anterior abdominal wall and the scrotum or labia majora. Plate N250 or TG5-4 shows the inguinal ligament going from anterior superior iliac spine to pubic tubercle. Be careful when skinning the scrotum because there is little fat and you want to leave the superficial (dartos) fascia intact for now (plates N387 or TG6-31 and N390). Plates N249 or TG5-2, N256 or TG5-2, and N500 or TG3-22 show the superficial epigastric, superficial circumflex iliac, and superficial external pudendal veins and arteries (all branches off the femoral artery or vein) in the subcutaneous tissue. Plates N266 or TG5-37 and N546 or TG3-70 show the superficial inguinal lymph nodes. Plate N249 or TG5-2 labels the fatty (Camper's) and membranous (Scarpa's) layers of superficial fascia. Cut through both layers at the umbilicus level and you can insert your hand beneath the membranous layer of superficial fascia, but superficial to the deep fascia. This membranous layer attaches to the pubic crest, pubic tubercle, fascia lata (N249 or TG5-2), and iliac crest. Plates N387 or TG6-31 and N390 (bottom) show the superficial (dartos) fascia of the scrotum, which is continuous with the membranous layer. Plates N257 or TG5-2 and N258 show the segmental cutaneous nerves of the abdominal wall. Plates TG3-25 and N498 or TG3-14 show the iliohypogastric and subcostal nerves at their origin, plate N267 or TG5-38 follows the course of these nerves, and plate N257 or TG5-2 shows cutaneous branches crossing the iliac crest. Remove the subcutaneous tissue while preserving the nerves and blood vessels you have found.

Step 3. Clean and examine the external abdominal oblique and its parts. (Play movie)

Plate N249 or TG5-2 shows the external abdominal oblique muscle, which is covered with deep investing fascia. Plates N387 or TG6-31 and N390 (bottom) show the continuation of this fascia as the external spermatic fascia (see the picture from objective 8-it is extremely helpful). Plate N387 or TG6-31 shows the external spermatic fascia extending from the superficial (external) inguinal ring. Plate N249 or TG5-2 shows the muscular and aponeurotic parts of the external abdominal oblique. Plates N249 or TG5-2 and N260 label the intercrural fibers and plate N259 or TG5-10 labels the medial and lateral crura (sing. crus). Plates N249 or TG5-2 and N250 or TG5-4 label the inguinal ligament. Plates N249 or TG5-4 and N260 or TG5-8 label the superficial inguinal ring. Plates N497 or TG3-25 and N498 or TG3-14 show the ilioinguinal nerve at the lumbar plexus and plates N257 or TG5-2 and N267 or TG5-38 show the course of this nerve and its anterior scrotal or labial branch being given off and passing through the superficial inguinal ring. Plates N250 or TG5-4 and N260 show the inguinal ligament being formed. Plate N260 also shows the ilioinguinal nerve and spermatic cord (round ligament of uterus in female) being transmitted through the superficial inguinal ring. Next, reflect the external abdominal oblique medially by cutting it from its costal attachments and its attachment to the iliac crest using a vertical incision (N249 or TG5-2). Do not cut too deeply because you want to separate this muscle from the internal abdominal oblique (N250 or TG5-4). Next cut horizontally from a point above the anterior superior iliac spine to a point above the midpoint of the superficial inguinal ring. Separate the external (N249 or TG5-2) and internal abdominal obliques while noticing that the aponeurosis of the external abdominal oblique fuses with the internal abdominal oblique muscle medially. Plates N387 or TG6-31 and N390 show the external spermatic fascia (continuous with the external abdominal oblique). Now continue the cut through the external abdominal oblique downward towards the superficial inguinal ring and reflect the muscle. Also, reflect the external spermatic fascia from the covering of the spermatic cord or round ligament (very carefully, see plates N387 or TG6-31 and N390).

Step 4. Clean and examine the internal abdominal oblique and transversus abdominis, their parts and specializations. (Play movie)

Plate N267 or TG5-38 (and N257 or TG5-2) shows the iliohypogastric and ilioinguinal nerves piercing the internal abdominal oblique muscle. You should now be able to find these nerves. Plate N174 or TG1-13 identifies the thoracolumbar fascia and plate N250 or TG5-4 shows the internal abdominal oblique attaching to the inguinal ligament. Plates N250 or TG5-4 and N259 or TG5-10 (top) identify the falx inguinalis (conjoint tendon). Plates N259 or TG5-10 (top), N260, N387 or TG6-31, and N390 (bottom) show the cremaster muscle as a continuation of the internal abdominal oblique. Reflect the internal abdominal oblique from the thoracolumbar fascia (N174 or TG1-13) by making a cut vertically from the ribs to the iliac crest and then horizontally toward the umbilicus (similar to how you reflected the external abdominal oblique). This muscle is difficult to separate from the transversus abdominis (N251 or TG5-05). It may be made easier to separate the muscles by trying to find the segmental nerves (N257 or TG5-2 and N258) that run in a plane between the two muscles. Plate N255 shows the ascending branch of the deep circumflex artery (deep circumflex iliac artery branches off the external iliac artery in plate N253 or TG5-7). Compare plates N257 or TG5-2 and N258 (segmental nerves) to plates N257 or TG5-2 and N267 or TG5-38 (ilioinguinal and iliohypogastric nerves). Notice the segmental nerves run between internal abdominal oblique muscle and transversus abdominis while the other two nerves pierce internal oblique to run between the internal and external abdominal oblique muscles. Plate N252 or TG5-6 shows the rectus sheath above and below the arcuate line (will be discussed more later).

Step 5. Open the rectus sheath and examine it and the rectus abdominis. (Play movie)

Open the rectus sheath by a vertical incision on both sides to expose the rectus abdominis and the tendinous intersections (you want to see the view on the right side of plate N250 or TG5-4). Next, make a vertical midline cut to reflect the rectus muscles laterally and reveal the transversalis fascia (right side of plate N251 or TG5-05). Plates N255, N256 or TG5-2, and N257 or TG5-2 show the relations of veins, arteries, and nerves to the rectus muscle and sheath. Plate N191 or TG4-09 shows the source of the superior epigastric artery (internal thoracic) and plate N253 or TG5-07 shows the source of the inferior epigastric artery (external iliac). Plate N251 or TG5-05 shows these arteries anastomosing.


Updated: 21 November 2011