Template:Abdominal Wall Muscle Timeline table

Carnegie stage 14 (E33) the mesoderm of the primary body wall was noncompact and it has coalesced in the ventral midline to create the abdominal cavity in which liver and stomach were seen at low magnification. Development of the CS 14 embryo was similar to the E10.5 mouse embryo and the dermomyotomes that are derived from somites have been formed.

Carnegie stage 16 (E40) the extent or distance of the migration was about 25% of the hemicircumference of the abdominal cavity. As seen in the mouse, the lateral plate mesoderm has become more condensed and thicker in the area around the myoblasts. The primary abdominal wall ventral to this region was thinner and less dense. This suggests that not only myoblasts but also the connective tissue may migrate into the primary body wall or may have active cell proliferation.

Carnegie stage 17 (E42) The histological appearance of the human abdominal wall at CS 17 was strikingly similar to the mouse at E11.5 with cells now having migrated approximately 50% of the distance to the ventral midline. Inner and outer layers were not discernible yet.

Carnegie stage 18 (E44) the separation of the myoblasts into distinct inner and outer layers became evident, and appeared to be equivalent to those in the E12.5 mouse embryo in terms of overall histological appearance and distance migrated by the myoblasts. The myoblasts in both the inner and outer layers began to exhibit unidirectional orientation. The abdominal wall was thicker (500 μm) in the region where secondary structures were forming compared with the primary body wall region (260 μm). In the more dorsally positioned regions, the outermost layer of connective tissue comprised approximately half of this thickness.

Carnegie stage 19 (E48) Segregation of the myoblasts into four distinct muscle groups was evident by CS 19 with unidirectional orientation of myoblasts. The myoblasts migrated over half of the distance to the ventral midline. The abdominal wall remains thickest in the area where the muscles migrated and again the outermost layer of connective tissue comprises approximately half of the total thickness of the abdominal wall in this region. In contrast the primary abdominal wall that is ventral to the migrating myoblasts was noticeably thinner. Unlike the mouse where the rectus is not segregated from the other muscles until reaching the midline, the human rectus was completely separated after migrating over half the distance to the midline.

Carnegie stage 21 (E54) the myoblasts have reached the ventral midline and myotubes were present and oriented uniformly within all muscle groups. The rectus abdominis formed distinct bundles of muscle indicating that development and differentiation of this muscle were more prominent in humans than in mice. Similar to the mouse embryo at E14.5, the connective tissue layers comprised the majority of the thickness of the abdominal wall at CS 21. Furthermore, the outermost layer of connective tissue accounted for the majority of this thickness.

Carnegie stage 23 (E58) the rectus muscle was forming 2 or 3 distinct layers and myotube orientation remained uniform in all muscles. The external oblique and internal oblique started to expand in terms of thickness whereas the transversus remained a thin layer of muscle. The thickness of the connective tissue was reduced similar to that in the mouse at E15.5. The orientation of connective tissue layers in the obliques and transversus abdominis was dorsal to ventral.