Catena Aurea on Matthew 1:1: Leo the Great

We do not speak of Christ as man in such a sort as to allow that any thing was wanting to Him, which it is certain pertains to human nature, whether soul, or rational mind, or flesh, and flesh such as was taken of the Woman, not gained by a change or conversion of the Word into flesh.

These three several errors, that thrice false heresy of the Apollinarists has brought forward. Eutyches also chose out this third dogma of Apollinaris, which denying the verity of the human body and soul, maintained that our Lord Jesus Christ was wholly and entirely of one nature, as though the Divine Word had changed itself into flesh and soul, and as though the conception, birth, growth, and such like, had been undergone by that Divine Essence, which was incapable of any such changes with the very and true flesh; for such as is the nature of the Only-begotten, such is the nature of the Father, and such is the nature of the Holy Ghost, both impassible and eternal.

But if to avoid being driven to the conclusion that the Godhead could feel suffering and death, he departs from the corruption of Apollinaris, and should still dare to affirm the nature of the incarnate Word, that is of the Word and the flesh, to be the same, he clearly falls into the insane notions of Manichaeus and Marcion, and believes that the Lord Jesus Christ did all His actions with a false appearance, that His body was not a human body, but a phantasm, which imposed on the eyes of the beholders.

But what Eutyches ventured [margin note: Id. Ep. 35 ad Julian] to pronounce as an episcopal decision, that in Christ before His incarnation were two natures, but after His incarnation only one, it behoved that he should have been urgently pressed to give the reason of this his belief.

I suppose that in using such language he supposed the soul which the Saviour took, to have had its abode in heaven before it was born of the Virgin Mary [ed. note, e: This opinion, which involves Nestorianism, the opposite error to Eutychianism or Monophysitism, is imputed to Eutyches by Flavian, ap. Leon. Ep. xxii. 3. Ephraem, Antioch, ap Phot. p. 805. Leont. de Sectis 7 init].

This Catholic hearts and ears endure not, for that the Lord when He came down from heaven shewed nothing of the condition of human nature, nor did He take on Him any soul that had existed before, nor any flesh that was not taken of the flesh of His mother. Thus what was justly condemned in Origen [ed. note, f: Vid. Origen in Joan. t. i. n. 37. t. xx. n. 17. Patriarch. ii. 6. n. 4. ix. Cels. i. 32, 33], must needs be rebuked in Eutyches, to wit, that our souls before they were placed in our bodies had actions not only wonderful but various.