Transversalis, Endoabdominal, Endothoracic Fascia: Who's Who?

Abstract

In Terminologia Anatomica of 1998, the fasciae of the trunk are listed as parietal, extraserosal, and visceral. Parietal fascia is defined as the fascia located outside the parietal layer of a serosa (e.g., pleura, peritoneum) lining a body wall cavity. The parietal fascia of the thorax is endothoracic fascia, and that of the abdomen is endoabdominal fascia. According to Terminologia Anatomica, endoabdominal fascia comprises: 1) transversalis fascia and 2) investing abdominal fascia: deep, intermediate and superficial. Thus, transversalis fascia is the innermost layer of endoabdominal fascia and, consequently, not synonymous with it. We assert that transversalis fascia is the inner epimysium of transversus abdominis muscle; no separate deep investing fascia exists. Embryologically, deep, intermediate and superficial layers of investing fascia are produced as muscular primordia–originating from somites invading somatopleura–penetrate somatic wall connective tissue, and thus obtain epimysium on either side, which give layers of investing fascia. In the thoracic wall, muscle layers are not separated and no distinct investing fasciae are found on them. Furthermore, in the thorax extraserosal fascia does not exist. Therefore, only endothoracic fascia is found on the inner side of the innermost intercostal muscle, which is deprived of investing fascia, to separate this muscle from pleura.