88
ALFRED J . COULOMBRE
O'Rahilly and Meyer, 1959). This is the directional membrane along
whose posterior surface mesenchymal cells will migrate to form the
posterior epithelium of the cornea. The acellular deposit between this
boundary and the posterior surface of the epithelium is called the postepithelial layer (birds: Kessler, 1877; Ladijenski, 1915; Laguesse, 1926;
Hagedoorn, 1930; O'Rahilly and Meyer, 1959; mammals: Mann, 1950;
Medvedeva, 1955). In forms such as the rat (Medvedeva, 1955) and the
rabbit (Rabl, 1900) where mesenchyme is present from the outset
beneath the anterior epithelium, the postepithelial layer develops late
and is very thin. I n the majority of species that have been investigated,
however, the postepithelial layer develops in the absence of such cells
(Levi, 1926). This fact, together with the close association of this layer
with the epithelium, led most of the earlier investigators who did
descriptive studies (Laguesse, 1923a, b ; Levi, 1926; Mann, 1931;
Migazzo, 1932) to conclude that it was synthesized by the epithelium.
Neifach (1952d) has demonstrated experimentally that the anterior
epithelium is the source of the postepithelial layer. By removing the
limbic area of the cornea of the chick embryo he isolated the epithelium
and the underlying postepithelial layer from the peripheral source of
mesenchyme cells before these had an opportunity to migrate in. Subsequently the postepithelial layer, in contact only with the cells of the
corneal epithelium, continued to increase in thickness.
The composition and structure of the postepithelial layer is of interest
because the stroma develops within it. I t has a fibrillar (Neüschuler,
1931; Redslob, 1935; Watzka, 1935; Iasvoin, 1939) or laminar (Ladijenski, 1915; Laguesse, 1923a, b) organization with the fibrous lamellae
disposed parallel to the overlying epithelium. In the chick embryo it
increases in thickness from 1-4 μ at 88-91 h of incubation to 9·5 μ at 120
h (Migazzo, 1932). Ladijenski (1915) described the fibrils in each lamella
as disposed orthogonally with respect to those in adjacent lamellae.
Fibrils in adjacent lamellae did not interlace. Ladijenski speculates that
the internal structuring of the extracellular compartment of the stroma
is thus laid down in miniature, and that, following the invasion of
stromal fibroblasts, the fibrils of this matrix are simply enlarged by the
deposition of collagen to form the fiber matrix which is typical of the
adult cornea. In the chick embryo the earliest lamellae are laid down
during the 3rd day of incubation (Laguesse, 1923b). The number of
lamellae increase to ten or fifteen early on the 5th day, and there are
twenty at the beginning of the 6th day (Laguesse, 1923a). Laguesse
also saw the orthogonal ply described by Ladijenski and speculated that
the corneal epithelium was responsible not only for the deposition of
these fibrils, but also for their orderly orientation into orthogonally
disposed lamellae. An attempt to confirm these remarkable observations
ALFRED J . COULOMBRE
O'Rahilly and Meyer, 1959). This is the directional membrane along
whose posterior surface mesenchymal cells will migrate to form the
posterior epithelium of the cornea. The acellular deposit between this
boundary and the posterior surface of the epithelium is called the postepithelial layer (birds: Kessler, 1877; Ladijenski, 1915; Laguesse, 1926;
Hagedoorn, 1930; O'Rahilly and Meyer, 1959; mammals: Mann, 1950;
Medvedeva, 1955). In forms such as the rat (Medvedeva, 1955) and the
rabbit (Rabl, 1900) where mesenchyme is present from the outset
beneath the anterior epithelium, the postepithelial layer develops late
and is very thin. I n the majority of species that have been investigated,
however, the postepithelial layer develops in the absence of such cells
(Levi, 1926). This fact, together with the close association of this layer
with the epithelium, led most of the earlier investigators who did
descriptive studies (Laguesse, 1923a, b ; Levi, 1926; Mann, 1931;
Migazzo, 1932) to conclude that it was synthesized by the epithelium.
Neifach (1952d) has demonstrated experimentally that the anterior
epithelium is the source of the postepithelial layer. By removing the
limbic area of the cornea of the chick embryo he isolated the epithelium
and the underlying postepithelial layer from the peripheral source of
mesenchyme cells before these had an opportunity to migrate in. Subsequently the postepithelial layer, in contact only with the cells of the
corneal epithelium, continued to increase in thickness.
The composition and structure of the postepithelial layer is of interest
because the stroma develops within it. I t has a fibrillar (Neüschuler,
1931; Redslob, 1935; Watzka, 1935; Iasvoin, 1939) or laminar (Ladijenski, 1915; Laguesse, 1923a, b) organization with the fibrous lamellae
disposed parallel to the overlying epithelium. In the chick embryo it
increases in thickness from 1-4 μ at 88-91 h of incubation to 9·5 μ at 120
h (Migazzo, 1932). Ladijenski (1915) described the fibrils in each lamella
as disposed orthogonally with respect to those in adjacent lamellae.
Fibrils in adjacent lamellae did not interlace. Ladijenski speculates that
the internal structuring of the extracellular compartment of the stroma
is thus laid down in miniature, and that, following the invasion of
stromal fibroblasts, the fibrils of this matrix are simply enlarged by the
deposition of collagen to form the fiber matrix which is typical of the
adult cornea. In the chick embryo the earliest lamellae are laid down
during the 3rd day of incubation (Laguesse, 1923b). The number of
lamellae increase to ten or fifteen early on the 5th day, and there are
twenty at the beginning of the 6th day (Laguesse, 1923a). Laguesse
also saw the orthogonal ply described by Ladijenski and speculated that
the corneal epithelium was responsible not only for the deposition of
these fibrils, but also for their orderly orientation into orthogonally
disposed lamellae. An attempt to confirm these remarkable observations