Figure 1-23
Sacrospinalis (erector spinae) muscles of the back.

Identify the long longitudinally running, bilateral erector spinae muscle. The lower portion of this muscle has been reflected to permit a laminectomy for the exposure of the spinal cord. Replace it to its natural position. (Figure 1-23)

Follow the erector spinae from its inferior attachment. Three poorly defined columns appear as the muscle ascends:

• The iliocostalis, the most lateral muscle column, is best observed in the midthoracic region
.
• The longissimus muscle medial to the iliocostalis is the longest of the erector spinae group and runs from pelvis to head
.
• The spinalis is the shortest and most medial muscle of the erector spinae group and is well defined in the thoracic region
.