The role of the medulla in the differentiation of the otic vesicle

Inherited diseases of the inner ear in man in the light of studies on the mouse.

“…Once this capacity has been acquired it will continue to develop in the normal direction for a limited time even when transplanted to some other part of the embryo. When the ear vesicle stage is reached the hind brain comes in as the dominant inductive influence (Waddington, 1937;Harrison, 1945;Yntema, 1950;Detwiler and van Dyke, 1950). The vesicle will not grow normally unless it is in contact with a certain region of the medulla.…”

“…Kaan (1938) believed that after its formation the capsule exerted reciprocal inductive influence on further differentiation of the ear, for when the capsule is not present the ear does not differentiate normally; but this view is not tenable, because the fact that a labyrinth did not form a capsule is a sign that it is abnormal in some way and hence cannot be expected to differentiate normally. Moreover, Detwiler and van Dyke (1950) have shown that, when the relevant part of the medulla is removed and the placode allowed to form an abnormal labyrinth, it forms a capsule, but its further differentiation is abnormal just the same.…”

Developmental Physiology

“…The role of the prechordal mes oderm in induction of the forebrain in amphibians has been reinvestigated by Gallera (71). The role of the medulla in inducing and controlling normal ear development has been demonstrated by Detwiler & Van Dyke" (72,73,74) and Yntema (75).· The time at which the reacting system becomes "at tuned" to the inductor (i.e., becomes "competent") has been shown in the case of lens induction in A mblystoma to occur during the 'open neural fold stage [Liedke (76)J. The dependence of extrinsic eye muscle development upon the optic cup and the independence of the lids and lacrimal glands have been shown by Amprino (77,78).…”

Determination of the embryonic inner ear

“…If the hindbrain is replaced at the 4 somite stage with mesencephlon/anterior spinal cord, ears form in the right place but do not differentiate (Detwiler, 1948;Detwiler and van Dyke, 1950). This could be an exhibition of specification (or more likely determination) as by the stage that the hindbrain had been removed, the ectoderm may already have been determined to form the early stages of an ear.…”