Imaging anatomy and new physiological concepts of the puborectalis muscle
In 1897, XXXX found a U-shape muscle, which circled the rectum and thus was called the puborectalis muscle, under the pubococcygeus. Most modern experts still consider it as one portion of the levator ani muscle [7]. In 1980, XXXX thought it had the function as sphincter and incorporated it into the external anal sphincter [8]. After 2007, XXXX et al obtained MRI images, in which the puborectalis muscle circled the vertical portion of the levator ani muscle first, the vertical portion of the levator ani muscle then circled urethra, vagina, and anorectum [3]. Our subsequent researches revealed that the puborectalis muscle is a completely independent muscle bundle. There was a clear anatomical interface between it and the levator ani muscle, and another interface between it and the deep external sphincter [6]. CT defecography results showed that the puborectalis muscle also had multiple functions, such as shrinking the urogenital hiatus, elevating the pelvis and anus [4]. When the puborectalis muscle was shrinking, all the interfaces between the urethra, vagina and anorectum would be compressed and above organs would be suspended anterosuperiorly. Therefore, its main function is shrinking the hiatus, elevating the pelvis and anus.
In 1979, XXXX also indicated that the puborectalis muscle had an inferior extended portion, which was one of the components of the conjoined longitudinal muscle [9]. However, our MRI images showed that the puborectalis muscle was a U-shape muscle without an inferior extended portion. It suggested that XXXX possibly misread the histological slide [6].
New imaging anatomy concepts of the external anal sphincter
In 1769, XXXX named the external anal sphincter and thought that it consisted of subcutaneous, superficial and deep components. In the following hundreds of years, the controversy of portions of the external anal sphincter never stopped [7]. In 1979, the controversy was aroused again when XXXX included the puborectalis muscle in the external anal sphincter. In 1999, XXXX et al conducted 100 cases of inner-anus coils in a MRI research and approved that it consisted of two portions, the subcutaneous portion and the superficial portion [11]. In 2005, the 39th edition of Gray’s Anatomy accepted the fact that there were only two portions included in the external anal sphincter [13]. In the same year of 2005, however, Hsu’s general MRI research showed that the external anal sphincter consisted of three portions [14]. In 2009, XXXX et al confirmed again that the external anal sphincter consisted of three portions. They also found that the blind zone of inner-anus coils in MRI images was the reason why XXXX et al misestimated there were only two portions. Our most important finding is that the subcutaneous portion of the external sphincter, which is inferior to the anal canal, forms a cutaneous muscle loop with perianal skin and blocks the inferior orifice of the anal canal [6].
New imaging anatomy concepts of anal canal area and perianal area
In 1888, the portion of rectal ampulla, which suddenly became thinner downwards, was named by XXXX as anal canal. In 1998, XXXX thought that the anal canal was circled by the internal anal sphincter and the external anal sphincter [15], which made the concept of anal canal area and perianal area more ambiguous. On MRI images, there is a clear anatomical interface between the rectum with its extended portion and the pelvic floor. Therefore, we name the extended portion of rectum as anal canal. The medial part of this interface is so called anal canal area and the lateral structure and tissues are called perianal area. The anal canal area comprises mucosa, submucosa and anorectal smooth muscle [6]. In microscope, the anorectal smooth muscle can even be classified as the internal anal sphincter and the longitudinal rectal muscle fiber bundle. However, the rare amount of the longitudinal rectal muscle fiber bundle makes it hardly layered [16]. There is a clear anatomical interface between anal canal area and perianal area. This indicates that the rectum and the anal canal can be dissected from pelvic floor. This finding allows a new idea for anorectal resection and reconstruction of enteroproctia.

耻骨直肠肌的影像解剖和生理新概念
1897年XXXX在耻尾肌的下方发现了一个U形肌肉，因其“包绕直肠”，被称为耻骨直肠肌（the puborectalis muscle），至今多数学者仍将其视为提肛肌的一部分[7]。1980年XXXX认为它有括约肌之功能，遂将其划归肛门外括约肌[8]。2007年以后，XXXX等获得的MRI图像显示，耻骨直肠肌先包绕提肛肌垂直部，提肛肌垂直部再包绕尿道、阴道和直肠肛门[3]。我们的后续研究显示耻骨直肠肌是一个完全独立的肌肉束，它与提肛肌和深部外括约肌之间均有明确的解剖分界面[6]；CT排便造影显示耻骨直肠肌还具有缩小泌尿生殖裂孔、提盆和提肛多重功能[4]。当耻骨直肠肌缩短时，尿道、阴道和直肠肛门交界部都会受到挤压，并将这些器官向前上方悬吊。因此，它的主要作用是缩裂孔、提盆和提肛。
1979年XXXX还认为耻骨直肠肌有一个下延部，该下延部参与了联合纵肌的构成[9]。然而，我们的MRI图像显示耻骨直肠肌是一个U形肌，并无下延部，提示XXXX误读了组织学切片[6]。
肛门外括约肌的影像解剖新概念
1769年，XXXX命名了肛门外括约肌（the external anal sphincter），并认为它是由皮下部、浅部和深部3部分组成的；此后的数百年间，肛门外括约肌可以分为几个部分，争议不断[7]。1979年XXXX将耻骨直肠肌划归肛门外括约肌，再次引起争议。1999年XXXX等人通过100例肛内线圈MRI研究，证实它是由皮下部和浅部2部分构成的[11]；2005年格氏解剖第39版也接受了肛门外括约肌只有2部分这一“事实” [13]。也是在2005年，Hsu等人的常规MRI研究却显示肛门外括约肌是由3部分构成的[14]。2009年XXXX等再次证实肛门外括约肌是由3部分构成的，同时发现肛内线圈MRI的盲区导致XXXX等人将其误判为2部分；我们最重要的发现是皮下部外括约肌位于肛管下方，与肛周皮肤形成一个皮肌袢样结构，封堵在肛管下口上[6]。
肛管部和肛周部的影像解剖新概念
1888年XXXX将直肠壶腹部向下突然变细的部分命名为肛管。1998年XXXX认为肛管被肛门内括约肌和肛门外括约肌两个肌性管所包绕[15]；这使得肛管部和肛周部的概念变得极其模糊。在MRI图像上，直肠及其延续部与盆底之间有一个明确的解剖分界面；因此，直肠的延续部被我们称之为肛管，我们还将这个分界面以内的部分称为肛管部，以外的组织结构称为肛周部；肛管部是由粘膜层、粘膜下层和肛门直肠平滑肌层构成的[6]。在显微镜下，肛门平滑肌层还可分为肛门内括约肌层和直肠纵肌纤维束，但是直肠纵肌纤维束非常稀少，几乎不能成层[16]。肛管部和肛周部之间存在明确的解剖分界面，说明直肠和肛管可以与盆底相互剥离。这个发现为直肠肛管切除术提供了新思路，也为人工肛门重建提供了新思路。