What was the last musical instrument that joined the mariachi?

By the end of the nineteenth century, in Cocula the vihuela, two violins, and the guitarró n ,which had replaced the harp, were the instruments of the Mariachi.

(A fines del siglo diecinueve, en Cocula, la vihuela, dos violines y la guitarra ,que había reemplazado al arpa, eran los instrumentos del Mariachi.