Rectus Abdominis
"Check out those rock hard Ab's."
Get Fit Today UK
The rectus abdominis muscle (commonly known as "abs") is a paired muscle running vertically on each side of the anterior wall of the human abdomen (and in some other animals). There are two parallel muscles, separated by a midline band of connective tissue called the linea alba (white line). It extends from the pubic symphysis/pubic crest inferiorly to the xiphisternum/xiphoid process and lower costal cartilages (5-7) superiorly.
It is contained in the Rectus sheath.
The rectus is usually crossed by three fibrous bands called the tendinous inscriptions. Colloqiual names for the appearance of a well-defined rectus abdominis include a six pack and "washboard abs", and often carry cultural connotations of superior physical fitness. While the "six pack" is by far the commonest configuration of the muscle bellies of the rectus, there exist rare anatomic variations which result in the appearance of eight (four per side) muscle segments ("eight pack"), ten, or (even rarer) asymmetrically arranged segments. All these variations are functionally equivalent.
This article was originally based on an entry from a public domain edition of Gray's Anatomy.