MD and not DM; PhD and not DPh

I've been wondering, who came up with the suffix "MD" or "PhD"? Sometimes the D that stands for "doctor" goes at the front, while other times it goes at the end. Of course, the roots go back to the Latin phrases:

M.D., from the Latin Medicinae Doctor meaning "Teacher of Medicine"
Ph.D. for the Latin Philosophiæ Doctor, meaning "teacher of philosophy"
or D.Phil., for the equivalent Doctor Philosophiæ

Here are some common doctorate degrees:

MD = Doctor of Medicine
PhD = Doctor of Philosophy (also written as DPhil)
DPH = Doctor of Public Health
PsyD = Doctor of Psychology
DO = Doctor of Osteopathic Medicine
OD = Doctor of Optometry
DSc or ScD = Doctor of Science
PharmD = Doctor of Pharmacy
DDS = Doctor of Dental Surgery
DMD = Doctor of Dental Medicine
DPM = Doctor of Podiatric Medicine