in most mammals its internal, but yeah, clitorises are pretty common. Ostriches have them too, oddly enough. Female hyenas have one big enoguh they unrinate and give birth through it.
At least in humans (other mammals too probably, but I'm not sure) they're actually the structure the penis forms from, in babies that have the right genetics for being sperm-producers. Everyone starts with a vagina and clitoris, the y chromosome usually* makes the vagina seal up, causes testicles form, and makes the clitoris enlarge and not become seperate from the urethra.
*there are exceptions that happen often enough we think they're just a normal, if uncommon, variation of human anatomy. See: complete androgen insensitivity syndrome, intersex