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. 

a subject of joke

Herman Melville's wife Elizabeth denied that bad reviews of Pierre (1852) made a hermit of her husband.  No, she wrote a relative in 1901, Herman was "naturally" reclusive and prone to shun "the bustling outside world."  Moreover, according to Melville's wife, the critical failure of Pierre

"was a subject of joke with him..."
(quoted in Pursuing Melville by Merton M. Sealts, Jr. at 215)

A joke!  How might Melville have joked about criticism like this

…Modern readers wish to exercise some little judgment of their own.... We are past the age when an artist superscribed his chef d’oeuvre with the judicious explanation, “this is a horse.” Mr. Melville longs for the good old times when the chorus filled the gaps between the acts with a well-timed commentary on the past, and a shrewd guess at the future.  (New York Herald, September 18, 1852, quoted here)

and these gems from the unfriendly review of Melville's Pierre in the Literary World, August 21, 1852:

"Mark the tragical result..."

"Mr. Melville may have constructed his story upon some new theory of art to a knowledge of which we have not yet transcended; he evidently has not constructed it according to the established principles of the only theory accepted by us until assured of a better, of one more true and natural than truth and nature themselves, which are the germinal principles of all true art.... The most immoral moral of the story, if it has any moral at all, seems to be the impracticability of virtue..."

"All the male characters of the book have a certain robust, animal force and untamed energy, which carry them through their melodramatic parts—no slight duty—with an effect sure to bring down the applause of the excitable and impulsive."

That's Evert Duyckinck coolly damning his sailor pal in print, so you can see why Hershel Parker thinks Melville's stoic joking must have masked a good deal of personal suffering.  (Herman Melville: A Biography, vol. 2 at 142)

How to reconcile the reception of Pierre as "a subject of joke" in Elizabeth's memory with the expected, natural human feelings of pain and bitterness?  Here's how:

 Cub, a Tragedy in Three Acts

In crossing the Platte this morning, the grizzly bear cub came on the scene in his final act.

It will be remembered by the patient and attentive future reader of this dry and methodical narrative, that its first appearance on any stage, was in "high" tragedy—that the first act embraced an unusual amount of sanguinary incident—that an innocent brother, (or sister,) being ruthlessly slain, and the baffled lady-mother left (unceremoniously) full of towering and demonstrative rage,— the imprisoned hero himself sank overwhelmed,—or in a well-acted counterfeit of death, (and was borne off, remember, on a "real" horse). That in the next act, (and three acts shall do for the tragedy of my bear,—originally they had but one,—but that was at the sacrifice of a goat,) 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.

To-day, then,—for I scorn anachronism— was performed the final act. The stage (wagon) was on "real water." Enraged at his wrongs, his losses, and his galling chain, the "robustious beast" acted in a ridiculous and unbearable manner; aye, ''tore his passion to tatters, to very rags,"—splinters; the stage (wagon) could not hold him: and finally in despair, he "imitated humanity so abominably," as to throw himself headlong, and so drown—or hang himself: (the author cannot decide which—even after a post mortem examination;—and so leaves the decision of this important point to the commentators).

My tragedy is all true,—and if not quite serious, has, as is proper, its moral;—but rather, as I have alluded to the primitive tragedy, let that "future reader" here imagine the entry of Chorus, and their song to Freedom! That dumb beasts prefer death to slavery! Liberty lost, they can die without the excitement of the world's applause, or hopes of a grateful posterity! (It is not possible, I think, that the cub could have known that I would immortalize him.)

"Scenes Beyond the Western Border," Southern Literary Messenger 19 (March 1853): 159 and
Scenes and Adventures in the Army (1857), 390

waters flowing through depths, emerging far away

Devil's Gate, Wyoming
Frederick Piercy, 1853

Hershel Parker, Melville Biography: An Inside Narrative:

"To declare that Melville was interested in bodies of water—lakes, ponds, flowing water, waterfalls, confluences of rivers, and oceans—is to announce the obvious. But there was more. Melville was fascinated by, perhaps haunted by, feelings of being subterranean, in the orlop deck, in vaults, in passages such as Giovanni Belzoni wormed his way through, in depths below depths as in the Hôtel de Cluny in Paris. He was particularly intrigued by waters that went subterranean and emerged far away." (15)

"You stand upon one side of what seems a deep green river, flowing through mountain passes to the sea..." (Omoo)

Thus liberated, the river enters a vast sunburnt plain; and, as if to take a last farewell of the romantic ridge, runs five or six miles to the foot of the solitary Independence Rock, thrown out like a grim sentinel upon the desert's boundary; then, as if warned of the salt and lava desolation beyond, turns again, and hastens to join the Platte, to aid in the evident struggle before it, with all the rocky powers of chaos and volcano.

Having thus, as from impulse, surrendered name and identity, and the excited contest over, they emerge from the secret and sublime mountain passes, in dreary unity, upon the boundless flatness of barren plains,—though some fleeting enjoyment of flowery savannas succeeds— before both are lost in Missouri's dark and turbid flood.

Farewell to thee, then, sweet daughter of Mountain! Thou smile upon our mother's melancholy face! Go,— with thy bright and blithe innocence,—like many another victim;—go purling merrily when you may, ignorantly happy, to the dark course of thy destiny. Thus do the Fates spin our warped life-threads,—thus do we weave its chequered or sombre web! [earlier version, Sept. 1852: "...ignorantly happy, to the chequered course of thy destiny. Thus do the silent Fates prepare for our warped life threads their sombre woof!]

.... Silvery gleams attract our sight—there is water—it is the river! In the midst of its secret, fierce course, a sweet glen has tempted it to a gentle pause on its soft bosom. It is then a river valley! Truly, close to our right, through an unsuspected chasm of wondrous depth, the happy Platte, having been somewhere secretly united to Sweet Water, has come to meet us, as witnesses to its triumph, or sharers in the excitement of a pleasure tour. Lowly, but bright and joyous in its life of motion and cumulative power, it advances, courting first all sweet and quiet recesses—yet daring all opposition to its wilful course. How we watch it now! Yonder, it sweeps in curves of beauty;—but suddenly lost, we gaze conjecturing where it may next appear; unexpectedly, it has paid a smiling visit to a grim mound, that stands modestly far aside; satisfied, it comes forth to new discoveries;—a determined barrier seems opposed ; but carelessly yet, it sports in some little meadows which can scarce be seen. Then it advances more seriously to a green hill, which seems bent in homage. But no! Nothing less than the loftiest mountain of proud rock, must give it passage! and through a narrow—a sublime chasm, it fiercely rushes forth to new labyrinths beyond.

September 1852, Scenes Beyond the Western Border; and
Scenes and Adventures in the Army

Update:  This lavish personification of the Sweetwater River has also to do with, besides surprise emergings from depths and labyrinths, a preoccupation with the confluence of rivers, here the Sweetwater and Platte, with a gloomy anticipation too of another confluence, the inevitable merging of the Platte and Missouri rivers.

"Why would he not seek out confluences of rivers, since from childhood he had walked on the Battery, seeing where the East River and the Hudson (or “North River”) merged after they poured separately into the bay?"  (Hershel Parker, Melville Biography: An Inside Narrative)