(3.48)

Now we’ll move on to look briefly at the principal nerves of the abdominal region. First we’ll see the nerves that provide the motor and sensory supply to the lateral and anterior abdominal wall.

These nerves are continuations of the lower intercostal nerves, from T7 downwards. Here are four of them. They emerge beneath the costal margin. Here’s the eleventh rib, here’s the start of the costal arch. The nerves run obliquely downwards and forwards in the plane between the transversus abdominis, and internal oblique muscles. The external oblique has largely been removed in this dissection.

Next we’ll look at the nerves of the posterior abdominal wall. These are derived from the lumbar plexus, a complex joining and re-branching of the anterior primary rami from the twelfth thoracic, to the fifth lumbar segment. The lumbar plexus lies behind and witihin the psoas major muscle. The nerves that arise from the lumbar plexus emerge from beneath psoas major, or through it.

Here are the subcostal nerve, which comes from T12, the ilio-hypogastric, and ilio-inguinal nerves, the lateral cutaneous nerve of the thigh, and the genito-femoral nerve. Between them, these provide sensation to the inguinal region, and to the anterior part of the upper thigh.

Here are two major nerves of the lower extremity: the femoral nerve, emerging lateral to psoas major, and the obturator nerve, emerging medial to it. The femoral nerve runs alongside psoas major, and passes beneath the inguinal ligament, just lateral to the femoral artery. The obturator nerve runs just below the pelvic brim, and enters the obturator canal.

The femoral and obturator nerves are shown in more detail in Volume 2 of this atlas. Lastly we’ll look at the principal autonomic nerves of the abdomen, the vagus nerves, the sympathetic trunks, and the aortic plexus.

Here’s the aortic bifurcation, here’s the upper part of psoas major, here’s the right crus of the diaphragm. Here’s the sympathetic trunk, emerging through the edge of the diaphragm, and running close to the vertebral bodies, down toward the pelvis.

Again, here’s the right crus of the diaphragm. Here are the divided celiac trunk, and superior mesenteric artery.

This is a large sympathetic ganglion. It’s connected to this smaller one, and to several others that have been removed in this dissection. Together they form the aortic plexus, which distributes sympathetic innervation to most of the abdominal viscera.

To see the vagus nerves as they enter the abdominal cavity we’ll look at a dissection in which the stomach has been left intact. This is the stomach. Here’s the esophagus. It comes through the diaphram here. Here are two branches of the right vagus nerve, also passing though the esophageal hiatus. The branches of the left vagus are out of sight round here.

The vagus nerves break up into many smaller branches which provide the parasympathetic supply to the stomach, the small and large intestine, and other abdominal organs.