362
G.
V. LOPASHOV AND O. G. STROEVA
mechanical firmness of the eye walls. In the mammalian sclera, the
scleral collagen appears first of all in the region of the limbus (Smelser
and Ozanicz, 1956). It is possible that collagen in mammals plays the
same role in corneal formation as the cartilaginous ring plays in birds.
In summary, corneal formation is closely related to its spatial localization and the mechanical tension in the system of the eye. By interaction
with the eye cup, the ectodermal epithelium lying over it forms the
post-epithelial cell-free layer which is the rudiment of the substantia
propria. After the invasion of mesenchyme cells there commence to
form in them primary argyrophylic fibrils which are later replaced
by definitive collagenous fibres. The structure of the anterior corneal
epithelium is determined by the underlying substantia propria while the
formation of fibrils in this latter proceeds under the influence of both
corneal epithelia. The formation of the Bowman's and Descemet's
membranes takes place as a result of the interaction between the epithelia and the corneal stroma. Mechanical tension, rising as a result of
the increasing intraocular pressure, develops tangential forces which
determine the orientation of the fibrils formed parallel to the corneal
surface and determine the thickness of the cornea. With differential
changes in the firmness of eye walls the action of the intraocular pressure
leads to a change of the primarily spherical eye, as a result of which the
corneal curvature acquires a lesser radius than the scleral segment.
Finally, the appearance of corneal transparency is related to the loss of
water and to the appearance in it of definitive collagen fibrils and
metachromatic mucopolysaccharides.
VI. Development of Mesenchymal Eye Envelopes
The eye rudiment is very early surrounded by the loose mesenchyme
which later on gives rise to the mesenchymal envelopes of the eye: the
choroid coat, the iris stroma and the sclera. The influence of the mesenchyme on the formation of the pigment epithelium has already been
mentioned (§111). We shall deal here with the origin of the mesenchyme
from which the eye envelopes are formed, and with the conditions
necessary for their formation.
Experimental investigations that have revealed the role played by the
neural crest in the origin of the mesenchyme and chromatophores
(Harrison, 1938; Hörstadius, 1950) raise the question as to the role such
ectomesenchyme may play in the development of the envelopes of the
eye. Transplanting eye rudiments from coloured chicks to the body
cavity of White Leghorns before and after the invasion of migrating
ectomesenchyme cells into the eye rudiments, Ris (1941) was able to
show that the pigmented cells of the choroid coat and iris arise from the
G.
V. LOPASHOV AND O. G. STROEVA
mechanical firmness of the eye walls. In the mammalian sclera, the
scleral collagen appears first of all in the region of the limbus (Smelser
and Ozanicz, 1956). It is possible that collagen in mammals plays the
same role in corneal formation as the cartilaginous ring plays in birds.
In summary, corneal formation is closely related to its spatial localization and the mechanical tension in the system of the eye. By interaction
with the eye cup, the ectodermal epithelium lying over it forms the
post-epithelial cell-free layer which is the rudiment of the substantia
propria. After the invasion of mesenchyme cells there commence to
form in them primary argyrophylic fibrils which are later replaced
by definitive collagenous fibres. The structure of the anterior corneal
epithelium is determined by the underlying substantia propria while the
formation of fibrils in this latter proceeds under the influence of both
corneal epithelia. The formation of the Bowman's and Descemet's
membranes takes place as a result of the interaction between the epithelia and the corneal stroma. Mechanical tension, rising as a result of
the increasing intraocular pressure, develops tangential forces which
determine the orientation of the fibrils formed parallel to the corneal
surface and determine the thickness of the cornea. With differential
changes in the firmness of eye walls the action of the intraocular pressure
leads to a change of the primarily spherical eye, as a result of which the
corneal curvature acquires a lesser radius than the scleral segment.
Finally, the appearance of corneal transparency is related to the loss of
water and to the appearance in it of definitive collagen fibrils and
metachromatic mucopolysaccharides.
VI. Development of Mesenchymal Eye Envelopes
The eye rudiment is very early surrounded by the loose mesenchyme
which later on gives rise to the mesenchymal envelopes of the eye: the
choroid coat, the iris stroma and the sclera. The influence of the mesenchyme on the formation of the pigment epithelium has already been
mentioned (§111). We shall deal here with the origin of the mesenchyme
from which the eye envelopes are formed, and with the conditions
necessary for their formation.
Experimental investigations that have revealed the role played by the
neural crest in the origin of the mesenchyme and chromatophores
(Harrison, 1938; Hörstadius, 1950) raise the question as to the role such
ectomesenchyme may play in the development of the envelopes of the
eye. Transplanting eye rudiments from coloured chicks to the body
cavity of White Leghorns before and after the invasion of migrating
ectomesenchyme cells into the eye rudiments, Ris (1941) was able to
show that the pigmented cells of the choroid coat and iris arise from the