In [10], Tutte introduced the concept of 3-connected matroids and proved the Wheels and Whirls Theorem, namely: wheels and whirls are the only 3-connected matroids without a single-element deletion or contraction that is 3-connected. Fifteen years latter, Oxley [6] was the pioneer in the study of a larger class of matroids known as the minimally 3-connected matroids. (A 3-connected matroid without a single-element deletion that is 3-connected is said to be minimally 3-connected.) Oxley [6] proved that a minimally 3-connected matroid M with at least four elements has at least