What's the difference between prefatory and prolegomenary?

Prefatory

Definition:

(a.) Pertaining to, or of the nature of, a preface; introductory to a book, essay, or discourse; as, prefatory remarks.

Example Sentences:

(1) We observed that, prefatory to myelination, SCs extended along the length of larger axons, apparently competing with adjacent SCs for axonal surface contact.
(2) Thus, several types of experiments demonstrate that SC myelin formation can be controlled by regulating the ability of the SC to assemble basal lamina, illustrating that acquisition of basal lamina is a crucial prefatory step for further SC differentiation.
(3) It is therefore prudent for the physician to insist upon a carefully worded written authorization, executed by the patient, prefatory to release of any such information.