John Trapp on Job 40:16

Verſe 16. Lo now his ſtrength is in his loines] Wherein he is ſo ſtrong, that he can beare a wooden Tower upon his back, and upon that two and thirty men ſtanding to fight there-from. In India, where the hugeſt Elephants are, they ride upon the bigger, plow with the leſſer, and carry great loads and burdens with both. For which and the like purpoſes,Junius. totus robuſtiſſimus eſt ſupernè & infernè. Howbeit God hath chiefly placed his ſtrength, not in any offenſive part (his head hath no horns, nor his feet no clawes to do miſchief with) but in his loynes, and about his belly.

And his force is in the navel of his belly] Which muſt needs be very hard undergirded, when ſo great weight is made faſt to his back. Naturaliſts obſerve, That the ſofteſt part of the Elephant is his belly; and therefore the Rhinoceros, (his deadly enemy) ſetteth upon him there with his crooked horn whetted againſt a Rock, and overcometh him; yet is he ſtronger in his belly then other Creatures are in the back: and therfore his Navel is here called Navels in the plural. His skin is exceeding hard and rough, ſo that an Arrow can hardly pierce it. Yet Eleazer, Machab. 6 ruſhing into the enemies Army, gat under an Elephants belly, (upon which he thought King Antiochus rode) and killed him, being himſelf cruſhed to death with the weight of the Beaſt falling upon him.