摘要传统意义上的外科解剖或局部解剖由两个基本元素构成，一是器官或组织，二是它们的血供。可是，这两者都被由筋膜和浆膜构成的“信封”所包绕，是为外科解剖的第三元素（the third component），长期以来被人们所忽略。这种遗漏或忽略是因分辨与识别不了、功能与意义不明所致。它的重新认识，将充实外科解剖或局部解剖学、肿瘤病理学、肿瘤外科学及其手术学。首先，“第三元素”的认识使外科解剖从器官解剖和血管解剖，进入到膜解剖，后者包括着广义的系膜和系膜床的解剖，也包括构成二者的浆膜和筋膜的解剖。第二，“第三元素”构成的信封样结构为“第五转移”提供了解剖学基础，该结构的破坏将导致系膜内肿瘤的“第五转移”泄露到手术野。第三，基于“第三元素”下的解剖学和病理学发展，临床上的胃肠肿瘤可分为系膜内癌、系膜边癌和系膜外癌3类。系膜外癌不属于外科根治范畴，防止癌泄露、降低系膜边癌和根治系膜内癌，是外科治疗的主要任务。因此，胃肠外科肿瘤根治手术可分为仅考虑淋巴结清扫的D手术、仅考虑系膜完整切除的C手术，和兼顾淋巴清扫与系膜完整切除的D＋C手术。

abstractsSurgical or local anatomy consists of two components conventionally, organs and their blood supply. In fact, they are enveloped by the fascia membrane and serous membrane. This is the third component in surgical or local anatomy, which is omitted by surgeons for many years. The omitted reasons are failed recognition and unknown function. Re-understanding of the third component in surgical or local anatomy will make some changes in the local anatomy, tumor pathology, oncology surgery and operations. Firstly, the third component makes surgical anatomy developed from organ anatomy, blood vessel anatomy to membrane anatomy, which consists of the mesentery in broad sense and its bed, both include serous membrane and fascia membrane. Secondly, the third component provides the basic membrane anatomy of envelop cavity of metastasis V , and the impairment of its integrity will induce the mesentery cancer leakage of metastasis V in the operation field. Thirdly, based on the development of anatomy and pathology of the third component, cancer of alimentary tract can be divided into 3 types, the cancer in the mesentery, the cancer at the mesentery edge and the cancer outside the mesentery. Cancer outside the mesentery is in the field of oncology except complication of primary lesion , such as bleeding, perforation and obstruction. The main task of surgeons is to prevent the cancer leakage during operation, improve the cancer at the mesentery edge and perform radical operation for the cancer in the mesentery. Finally, the principle of radical operation for the cancer of alimentary tract should include the primary lesion resection , systematical lymphadenectomy and complete mesentery excision. Therefore, these principles should be classified into three kinds:(1)D type operation, which is only the concern about lymphadenectomy at D2 or D3 level and does not care about the completeness of the mesentery; (2)C type operation, which is only the concern about completeness of the mesentery, with only high tie of blood vessels, which does not care about ligation at the bifurcation; (3) D+C type operation, which is not only the concern about ligation at the bifurcation, but also about the completeness of the mesentery. Many aspects will change with surgical developments, especially with the membrane anatomy, the third component.