The first to which we come is merely an allusion to the narrative of Matt.

ii; 'For Domitian feared the coming of the Christ as much as Herod.' Those therefore who take the statement of Eusebius to mean that Hegesippus used only the Gospel according to the Hebrews are compelled to seek for the account of the Massacre of the Innocents in that Gospel.

It appears however from Epiphanius that precisely this very portion of the first Gospel was wanting in the Gospel according to the Hebrews as used both by the Ebionites and by the Nazarenes.

'But if it be doubtful whether some forms of that Gospel contained the two opening chapters of Matthew, it is certain that Jerome found them in the version which he translated' [Endnote 141:1].

I am afraid that here, as in so many other cases, the words 'doubtful' and 'certain' are used with very little regard to their meanings.
In support of the inference from Jerome, the author refers to De Wette, Schwegler, and an article in a periodical publication by Ewald.