SOURCE: A Latin Reader by Basil Lanneau Gildersleeve. For more information and other versions, see the links list for Perry 137 and also the page at Aesopica.net.
READ OUT LOUD. Choose which marked text you prefer to practice with - macrons or accent marks - and read the text out loud until you feel comfortable and confident. Then, try reading the unmarked text at the bottom. It should be easy for you after practicing with the marked texts. :-)
MACRONS. Here is the text with macrons:
In cornū taurī parva sedēbat musca. Sī tē nimis gravō, inquit, statim āvolābō. Taurus respondet: Ubi es? Nihil sentiō.
ACCENT MARKS. Here is the text with accent marks, plus some color-coding for the words of three or more syllables (blue: penultimate stress; red: antepenultimate stress):
In cornu tauri parva sedébat musca. Si te nimis gravo, inquit, statim avolábo. Taurus respóndet: Ubi es? Nihil séntio.
UNMARKED TEXT. Here is the unmarked text - after practicing with the marked text that you prefer, you should not have any trouble with the unmarked text:
In cornu tauri
parva sedebat musca.
"Si te nimis gravo (inquit),
IMAGE. Here is an illustration for the story (image source), although it shows the fly in the cow's ear, rather than on the horn.