Axiom: On cutting through the abdominal wall, the encountering of a layer of loose areolar tissue is a signal that a change in the direction of muscle fibers is imminent. When you incise the abdominal wall, the direction of muscle fibers, the presence of areolar tissue, and the presence of nerves and of branches of the deep circumflex iliac artery all indicate the depth at which you have arrived.
Source: Boileau Grant JC. A Method of Anatomy: Descriptive and Deductive. 5th ed. Baltimore, Md: Williams & Wilkins Co; 1952:215.
January 2003. Arch Surg. 2003;138(1):75. doi:10.1001/archsurg.138.1.75