At ST IIIa.52.3 he [i.e., Aquinas] maintains that the whole Christ was in Hell after His death and before His resurrection, and considers the following argument to the contrary: "The body of Christ is part of Him. But the body of Christ was not in Hell. Consequently the whole Christ was not in Hell" (ST 3.52.3, obj. 1). He answers: "The Body that was then in the tomb is not part of the uncreated person, but of the assumed nature. Accordingly, the fact that Christ's body was not in Hell does not preclude the whole Christ's being there" (ST 3a.52.3 ad 1). If the body in the tomb is not part of the uncreated person of Christ, then the body is not part of Christ, since the uncreated person of Christ is nothing other than Christ Himself. Aquinas' point here is not just that while Christ's body was in the tomb, it was not a part of Christ. (If that were his point, he would say that the body that was then in the tomb was not (then) a part of the uncreated person of Christ, rather than that the body then in the tomb is not a part of His uncreated person.) For Aquinas, neither Christ's body nor any of its parts are parts of Christ, although they are parts of His assumed nature.
[Hughes, A Complex Theory of a Simple God. Cornell (Ithaca: 1989) 250-251]
Hughes understands this to mean that Aquinas holds that Christ as a person "never has any human bodily parts." Some of what Aquinas says, if not read carefully, could yield this conclusion, but I think a more careful reading gives us a better interpretation.
To understand Aquinas on this, we need to recognize that on his account of the descent into hell (hades), the whole person of Christ was in hades, because the soul of Christ was in hades, and the whole person of Christ was in the tomb, because the body of Christ was in the tomb. This last is a peculiar case. On Aristotelian principles, corpses usually have nothing to do (properly and strictly speaking) with persons: my body is really my body, but my corpse will not be my corpse in anything like the same sense. Indeed, my corpse will arguably not even be a body in quite the same sense. The case of Christ is a bit different, though. The divine Word assumes a human nature, which means that He assumes both body and soul. He didn't just assume a soul that happened to inform a body; He became flesh, assuming a body as well as a soul. Thus Thomas's point in the reply to the objection is that the person of Christ is not divided up into a body-part and a soul-part; rather, the person of Christ is wherever either the body or the soul are, because the person of Christ assumed both. The claim is not that the person of Christ has no parts (He does by way of the assumed nature), but that the person of Christ is not divided up according to the parts He has. The objector, after all, is claiming that since only part of Christ (the soul) was in hell, only part of the person of Christ was in hell, and Aquinas points out that this is an illicit inference. Instead, "the whole Christ was in the tomb, because the whole Person was there through the body united with Him, and likewise He was entirely in hell, because the whole Person of Christ was there by reason of the soul united with Him, and the whole Christ was then everywhere by reason of the Divine Nature." So the claim is not that the divine person has no parts, but that the divine person has no parts qua person (rather than qua person of this human nature). And as Hughes notes, Aquinas on occasion implies that Christ is constituted of a rational soul and a body (e.g., SCG 4.37). And this is not surprising, because Christ does have these. He has them by virtue of being a person with a human nature, just as we do. But this does not mean that when part of Christ is here and another part is there that Christ, as a person, is only partly here and partly there.
Granted, the distinction between the two can be subtle. But it makes for a considerable difference. On Aquinas's view, the divine Word on Holy Saturday was (1) everywhere by divine nature; (2) in the tomb by human nature insofar as it involved a body; and (3) in Hades by human nature insofar as it involved a soul. The Word was not divided up, because the Word is (1) divine; and (2) assumes the whole human nature and all its parts. So both the soul of Christ in Hades and the body of Christ in the tomb are the Word of God. It's just that they are the Word of God by virtue of being different parts of His human nature. The only thing death brought about was his ceasing to be a whole man, not his ceasing to be a whole person. Contrast this to a view in which the parts are not parts of Christ; then Aquinas's conclusion -- that the whole Christ is wherever soul and body both are -- could never get off the ground.
What Hughes is, in fact, doing is conflating two things that Aquinas sharply distinguishes: union of person and union of nature. Aquinas's point is always that the natures of Christ are united in and by a person, who has one necessarily and takes on another. Thus Christ exists, and by assuming the human nature, exists in human parts (body and soul). This contrasts with, say, the union of soul and body, which is a union of natures -- two things with certain features each become parts of a greater whole. Nor is this entirely strange. For some people, for entirely independent reasons, want to argue that in mereology we should distinguish the part-whole relation from the part-subject relation, as two different things. Parts divide up their wholes; but they don't divide up the subjects that have the parts. Rather, they (for lack of a better word) express them.
