<prompt> In the pathogenesis of otosclerosis, the disease process starts in:Periosteal layer of otic capsuleEndosteal layer of otic capsuleBone of otic capsule which develops from cartilageMucoperiosteum of the promontory  <response>: Otic capsule also called bony labyrinth has three layers: outer periosteal, inner endosteal and the middle bony. The bony layer which develops from cartilage and for some unknown reason bone of the otic capsule is absorbed and replaced by spongy vascular bone which later becomes sclerotic due to deposition of calcium. 