TEN FIGURES
Descriptions of the rectus slieatli contained in our textbooks of anatomy are singularly alike; they are stereotyped and oversimplified ; when these accounts recognize structural variation at all it is only in connection with the position of the linea semicircularis. It is regularly stated that in the area superior to the level of the linea semicircularis the internal oblique aponeurosis divides into two lamellae, one blending with the external oblique aponeurosis as it passes in front of the rectus muscle, the other fusing with the aponeurosis of the transversus as it passes behind the muscle ; it is further stated that in the ten-itory situated inferior to the level of the linea semicircular the aponeuroses of the three muscles join while coursing across the front of the rectus, leaving the latter's posterior surface in direct contact with the transversalis fascia. According to the same accounts the sheath is deficient in the thoracic region, the muscle resting on the costal cartilages posteriorly, covered anteriorly by the external oblique aponeurosis.
Actually irregularities in the composition of the laminae are common, with the result that the position, the outline, and the Contribution No. 307 from the Anatomical Labomtory of Northwestern University Medical School.