In the sequel to the 1994 original, Lloyd and Harry, played by Jim Carrey and Jeff Daniels, set out to find Harry's daughter who has been adopted. (Universal Studios)

Like the original 1994 “Dumb and Dumber,” the 20th anniversary sequel “Dumb and Dumber To” involves a transcontinental road trip. And yet despite scenes taking place in Rhode Island, Maryland, Kansas, Texas and spots in between, the story rarely turns its attention away from a region of a few square inches. With the persistence of an annoying brat hammering away on your front door, the film relentlessly, almost numbingly, focuses on the human body’s locus of excretory and sexual functioning.

This wearying, nearly two-hour marathon of crotch-centric humor opens with a sight gag about yanking a stubborn catheter out of a man’s urethra. And yet there is much more to come. What follows are literally dozens of references to orifices and sphincters and the things that can come out of (or go into) them. The high point — and I don’t mean that sardonically, it’s actually kind of funny — comes with a scene featuring Jim Carrey, reprising his role as the moron Lloyd Christmas, with his hand buried up to the wrist inside the pelvic cavity of an elderly woman in a nursing home.

He is looking for diamonds.

It is gems like this, evidently, that require the talents of six screenwriters, including co-directors Bobby and Peter Farrelly, the dynamic sibling duo whose films have ranged from the wickedly naughty (“There’s Something About Mary”) to the execrably inane (“The Three Stooges”). This one falls somewhere in between. Thank you, Sean Anders, Mike Cerrone, John Morris and Bennett Yellin, for changing forever my understanding of the terms “mudhole” and “dark matter.”

The plot, though it hardly seems of consequence, concerns the efforts of Lloyd and his cretinous best friend, Harry Dunne (Jeff Daniels), to track down a young woman (Rachel Melvin) who Harry believes to be his illegitimate daughter. As evidenced by the frequent shots of Daniels’s naked, widening, ­middle-aged derriere, Harry has not aged well and is in need of a kidney transplant from a relative.

Jim Carrey, left, Jeff Daniels, right, and Rob Riggle in a scene from "Dumb and Dumber To." (Hopper Stone/UNIVERSAL PICTURES/AP PHOTO)

Truth be told, the plot device seems little more than an excuse to mention urine, over and over.

A game Kathleen Turner is the woman’s mother and Harry’s ex-girlfriend, although “girlfriend” is probably not the right word here. The consistently misogynist script refers to her character, twice, as a “titanic whore.” And yes, the film is rated PG-13.

Along the way, the screenplay throws in a Zamboni, a scene implying bestiality and at least three opportunities for Carrey to say, in the voice of Sean Connery, some variation of “Bond . . . James Bond.” This, needless to say, is apropos of nothing, but is mildly amusing. Carrey, at least, can be counted on to make consistently silly faces and voices.

So maybe some of this is hilarious. Heck, maybe all of it is. It will not be everyone’s cup of tea, and it was not mine.

As Harry says near the beginning of the movie, “God’s got a pretty warped sense of humor.” If that’s the case, the Creator, in His infinite wisdom, might give this movie four stars. I, on the other hand, am just a man.

Dumb and Dumber To

½

(109 minutes, at area theaters) is rated PG-13 for pervasive crude and sexual humor, obscenity, views of bare buttocks and drug use.)