During sexual excitement of a bull, the muscle within the pelvic area, called the issues cavernosus muscle, will contract. Interesting, huh?
Well, if you're a soon-to-be veterinarian, or just merely curious on the science and anatomy of a bulls reproductive organs, then I guess you're going to have to watch these video tutorials on the dissection of a male bulls penis.
This highly educational video series covers the erection of a bull, the emission, and the ejaculation of a bull. The penis muscles are in full view here, so beware.