Princeton's WordNet(4.00 / 2 votes)Rate this definition: 1  unfathomable(adj) of depth; not capable of being sounded or measured. 2  abysmal, abyssal, unfathomable(adj) resembling an abyss in depth; so deep as to be unmeasurable. 3  unfathomable(adj) impossible to come to understand.
The rectus abdominis, transverse abdominis, external oblique and the internal oblique make up the abdominal muscles. The internal obliques are located just underneath the external obliques and allow you to bend from the side, as well as twist your torso.
External abdominal oblique muscle. The external abdominal oblique muscle is the largest and most superficial of the 3 paired, flat abdominal muscles. It arises from the lower 8 ribs and interdigitations of the serratus anterior muscle.he abdominal wall is composed of 5 paired muscles: 2 vertical muscles (the rectus abdominis and the pyramidalis) and 3 layered, flat muscles (the external abdominal oblique, the internal abdominal oblique, and the transversus abdominis muscles).