Jamieson, Fausset and Brown on Job 19:20

20. Extreme meagerness. The bone seemed to stick in the skin, being seen through it, owing to the flesh drying up and falling away from the bone. The Margin, "as to my flesh," makes this sense clearer. The English Version, however, expresses the same: "And to my flesh," namely, which has fallen away from the bone, instead of firmly covering it.

skin of my teeth--proverbial. I have escaped with bare life; I am whole only with the skin of my teeth; that is, my gums alone are whole, the rest of the skin of my body is broken with sores (Job 7:5; Psa 102:5). Satan left Job his speech, in hope that he might therewith curse God.