The outermost muscular layer of the lateral abdominal wall is made up from the external oblique muscles.  These two muscles arise from the outer parts of the lower 7 to 8 ribs on either side and extends anteroinferiorly to the anterior aspect of the iliac crests, pubic tubercle and to the linea alba in the midline. Towards the midline the muscle forms an aponeurosis.

Note that the direction of the fibres of the external oblique muscle (EO) can be appreciated using CT. Also labelled, rectus abdominis (RA); linea semilunaris (white arrowhead); linea alba (black arrowhead) and spermatic cord (arrow).