Matthew Poole and continuators on Job 40:16

16. Lo now, his strength is in his loins , and his force is in the navel of his belly .

He hath strength answerable to his bulk, but this strength by God's wise and merciful providence is not an offensive strength, consisting in or put forth by horns or claws, as it is in ravenous Creatures, but onely defensive and seated in his Loins▪ as it is in other Creatures, whereby he is rendred more serviceable to men by the carrying of vast burdens.

which though in the Elephant it be weaker than his loins, whence the Rhinoceros fighting with him aims at that part, yet hath a more than ordinary strength it it, as appears by the binding of the heaviest burdens under and about it. This also agrees to the Hippopotamus in an eminent degree, whose whole skin is noted by ancient Writers to be harder than any other Creatures and almost impenetrable.