Anal canal sphincters

Figure 4: There are two sphincters, the internal which is a thickening of the continuration of the circular muscle of the rectum. And the external which forms a complex with the pubo-rectalis and levator ani. Red levator ani, green, circular muscle of rectum and internal sphincter, cyan external sphincter, dark blue longitudinal muscle of rectum.

The anal canal has two main sphincters, these are termed the interal and external anal sphincters.