Objection 1. It seems that Christ did not receive His own body and blood, because nothing ought to be asserted of either Christ's doings or sayings, which is not handed down by the authority of Sacred Scripture. But it is not narrated in the gospels that He ate His own body or drank His own blood. Therefore we must not assert this as a fact.
Objection 2. Further, nothing can be within itself except perchance by reason of its parts, for instance. as one part is in another, as is stated in Phys. iv. But what is eaten and drunk is in the eater and drinker. Therefore, since the entire Christ is under each species of the sacrament, it seems impossible for Him to have received this sacrament.
Objection 3. Further, the receiving of this sacrament is twofold, namely, spiritual and sacramental. But the spiritual was unsuitable for Christ, as He derived no benefit from the sacrament. and in consequence so was the sacramental, since it is imperfect without the spiritual, as was observed above (Question 80, Article 1). Consequently, in no way did Christ partake of this sacrament.
On the contrary, Jerome says (Ad Hedib., Ep. xxx), "The Lord Jesus Christ, Himself the guest and banquet, is both the partaker and what is eaten."
I answer that, Some have said that Christ during the supper gave His body and blood to His disciples, but did not partake of it Himself. But this seems improbable. Because Christ Himself was the first to fulfill what He required others to observe: hence He willed first to be baptized when imposing Baptism upon others: as we read in Acts 1:1: "Jesus began to do and to teach." Hence He first of all took His own body and blood, and afterwards gave it to be taken by the disciples. And hence the gloss upon Ruth 3:7, "When he had eaten and drunk, says: Christ ate and drank at the supper, when He gave to the disciples the sacrament of His body and blood. Hence, 'because the children partook [Vulgate: 'are partakers' (Hebrews 2:14)] of His flesh and blood, He also hath been partaker in the same.'"
Reply to Objection 1. We read in the Gospels how Christ "took the bread... and the chalice"; but it is not to be understood that He took them merely into His hands, as some say. but that He took them in the same way as He gave them to others to take. Hence when He said to the disciples, "Take ye and eat," and again, "Take ye and drink," it is to be understood that He Himself, in taking it, both ate and drank. Hence some have composed this rhyme:
"The King at supper sits,
The twelve as guests He greets,
Clasping Himself in His hands,
The food Himself now eats."
Reply to Objection 2. As was said above (Question 76, Article 5), Christ as contained under this sacrament stands in relation to place, not according to His own dimensions, but according to the dimensions of the sacramental species; so that Christ is Himself in every place where those species are. And because the species were able to be both in the hands and the mouth of Christ, the entire Christ could be in both His hands and mouth. Now this could not come to pass were His relation to place to be according to His proper dimensions.
Reply to Objection 3. As was stated above (79, 1, ad 2), the effect of this sacrament is not merely an increase of habitual grace, but furthermore a certain actual delectation of spiritual sweetness. But although grace was not increased in Christ through His receiving this sacrament, yet He had a certain spiritual delectation from the new institution of this sacrament. Hence He Himself said (Luke 22:15): "With desire I have desired to eat this Pasch with you," which words Eusebius explains of the new mystery of the New Testament, which He gave to the disciples. And therefore He ate it both spiritually and sacramentally, inasmuch as He received His own body under the sacrament which sacrament of His own body He both understood and prepared; yet differently from others who partake of it both sacramentally and spiritually, for these receive an increase of grace, and they have need of the sacramental signs for perceiving its truth.
Source: Summa Theologica (New Advent)