Transversus abdominis m.

The transversus abdominis muscle is a muscle layer of the anterior and lateral abdominal wall which is deep to the internal oblique muscle. 

The transversus abdominis arises as fleshy fibers, from the lateral third of the inguinal ligament, from the anterior three-fourths of the inner lip of the iliac crest, from the inner surfaces of the cartilages of the lower six ribs, interdigitating with the diaphragm, and from the lumbodorsal fascia. It ends anteriorly in a broad aponeurosis, the lower fibers of which curve inferomedially, and are inserted, together with those of the internal oblique muscle, into the crest of the pubis and pectineal line, forming the inguinal aponeurotic falx, also called the conjoint tendon. In layman's terms, the muscle ends in the middle line of a person's abdomen.

Throughout the rest of its extent the aponeurosis passes horizontally to the middle line, and is inserted into the linea alba; its upper three-fourths lie behind the rectus muscle and blend with the posterior lamella of the aponeurosis of the internal oblique; its lower fourth is in front of the rectus abdominis.

The transversus abdominis is innervated by the lower intercostal nerves (thoracoabdominal, nerve root T7-T11), as well as the iliohypogastric nerve and the ilioinguinal nerve.