Our Gemara on amud beis continues to discuss that for a Meis Mitzvah (an abandoned corpse), even a Cohen Godol must bury him, and this need overrides the Cohanic prohibition to not be defiled from a corpse. It is evident from how Tosafos (“Hachi Garsinan De-Iylu”) analyzes the particular situation, that the Cohen Godol is permitted to engage in taking care of the corpse even when burial is not possible such as Yom Kippur. For example, moving the corpse away from the Sun to the shade so as to forestall rapid decomposition is also included in this directive. We see from here that the idea of Meis Mitzvah is not just burial, but it is anything that preserves the dignity of the human body after it is deceased. This is under the larger rubric of kvod haberiyos (see Rashi Berachos 20a, “aval metameh”.)

Rav Moshe Feinstein (Iggeros Moshe OC IV:69) uses this approach to explain a difficult section in the liturgy of the Yom Kippur prayers. (This comes courtesy of Rabbi Moshe Zev Granek’s Bais Vaad Halacha Center Shiur on Nazir 47.) 

In Yom Kippur Musaf we recite the chronicle of the 10 martyrs. We are told that Rabbi Yishmael picked up the severed head of Rabbi Shimon, crying bitterly. However, there is a technical problem. Rabbi Yishmael is a cohen and he was not allowed to defile himself by touching Rabbi Shimon’s head. We might say he was in such a grief that he did not know what he was doing. But that answer is not satisfactory because we mightnot be giving Rabbi Yishmael enough credit, assuming he would lost all self-control. Secondly, even if that were true, it would not be a great praise to record it for posterity in the liturgy. (Although the counter argument is that this, gufa, was his praise – how much he valued the life of his colleague.) Therefore, Rav Moshe used the opinion of Tosafos that we discussed above to explain that the special dispensation allowing a cohen to become defiled to take care of a Meis Mitzvah applies to all manner and form of showing honor to the deceased, and is not dependent on burial specifically. Therefore, at that tragic moment in time, the only type of eulogy and honor that rabbi Yishmael could show for his beloved fallen comrade, was to cradle his decapitated head, and lament bitterly.