his sentence-ending howl

In the mock tragedy "Cub," the captive bear cub turns defiant and frightens onlookers with his fierce "howl" of protest:

"... he came to life in a manner that might very well have been criticized as an overdone piece of stage-effect,—but that in fact, the spectators were much moved, and gave full credit to the dangerous passion of his howl.

Scenes Beyond the Western Border, (March 1853): 159 and
Scenes and Adventures in the Army (1857), 390

Verbally ("his howl") and thematically (imprisoned hero protests), the narrative from "Scenes Beyond the Western Border" replicates the situation of Enceladus the Titan in Melville's Pierre (1852).  In Pierre Melville's "form defiant" is a half-buried hillside boulder that looks like the defeated giant Enceladus, "writhing from out the imprisoning earth":

—turbaned with upborn moss he writhed; still turning his unconquerable front toward that majestic mount eternally—in vain assailed by him, and which, when it had stormed him off, had heaved his undoffable incubus upon him, and deridingly left him there to bay out his ineffectual howl. -- Pierre

Ooh! Meditating on these sentence-ending howls along with the playful use in "Scenes Beyond the Western Border" of language from negative reviews of Pierre (demonstrated here and here and here), not forgetting Harrison Hayford on Melville's Prisoners, I am about ready to declare victory and go home.