A new description of the anterior abdominal wall in man and mammals.

The ventral abdominal walls of 116 specimens (41 human and 75 from nine mammalian families) of various ages and both sexes were studied anatomically and histologically. In man, each abdominal aponeurosis was bilaminar, and each wall of the rectus sheath was trilaminar (plywood-like). The two layers of the internal oblique emerged, in part of its extent, superficial to the external oblique and also passed deep to the transversus abdominis. All the six aponeurotic layers were oblique and crossed the mid-line, forming the following digastric muscles: the two external obliques together, the two transversus abdominis muscles together, one internal oblique (anterior layer) with the opposite external oblique (posterior layer) and one internal oblique (posterior layer) with the opposite transversus abdominis (anterior layer). The linea alba might be considered less the insertion of the abdominal muscles, but rather the common area of decussation of their intermediate aponeuroses. In all mammals, the internal oblique aponeurosis passed either superficial to that of the external oblique or deep to that of the transversus. The transversus aponeurosis was always oblique and in all eutheria it split into two layers. All abdominal aponeuroses crossed the middle line forming digastric muscles between the two sides. The functional significance and surgical application of these findings are discussed.