The outermost muscle is the external oblique. Note the direction of the fasciculi in this muscle. The fasciculi are oblique to the trunk. Deep to the external oblique is the internal oblique. The fasciculi of the internal oblique run almost perpendicular to the fasciculi of the external oblique. The long segmented muscle running from the rib cage to the pubis is the rectus abdominis. The fibers of the rectus abdominis, like those of all "rectus" muscles, run parallel to the trunk.
The deepest muscle is the transverse abdominis. The fasciculi of the transverse abdominis run transverse to the trunk. Extra care must be taken to separate the extremely thin transverse abdominis, or you will cut through into the abdominal cavity. If you do cut into the abdominal cavity, stop! You will examine the digestive organs later.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.