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The optic vesicles project toward the sides of the head, and the peripheral part of each expands to form a hollow bulb, while the proximal part remains narrow and constitutes the optic stalk. [1] [2] Closure of the choroidal fissure in the optic stalk occurs during the seventh week of development. The former optic stalk is then called the optic ...
These diverticula make their appearance before the closure of the anterior end of the neural tube; [1] [2] after the closure of the tube around the 4th week of development, they are known as the optic vesicles. Previous studies of optic vesicles suggest that the surrounding extraocular tissues – the surface ectoderm and extraocular mesenchyme ...
The horse has a "visual streak", or an area within the retina, linear in shape, with a high concentration of ganglion cells (up to 6100 cells/mm 2 in the visual streak compared to the 150 and 200 cells/mm 2 in the peripheral area). [12] Horses have better acuity when the objects they are looking at fall in this region.
The optic vesicles then develop into the optic cup with the inner layer forming the retina and the outer portion forming the retinal pigment epithelium. The middle portion of the optic cup develops into the ciliary body and iris. [7] During the invagination of the optic cup, the ectoderm begins to thicken and form the lens placode, which ...
They limit a horse's rear vision but do not restrict the horse's view as much as blinkers do. Pacifiers are hoods with mesh cups over the eyes. Pacifiers protect the wearer's eyes from injury caused by dirt or stones being kicked up by horses ahead of the wearer during a race. They may be banned from use on wet days as they may clog up with mud ...
During embryonic development of the eye, the outer wall of the bulb of the optic vesicles becomes thickened and invaginated, and the bulb is thus converted into a cup, the optic cup (or ophthalmic cup), consisting of two strata of cells.
Simple horse twitch. A twitch is a device that is used to restrain horses during various stressful situations, such as veterinary treatment. [1] It is usually made up of a stick-like handle loop of chain or rope on the end, or a metal ring with a rope loop which is wrapped around the upper lip of the horse and tightened.
Improper closure of the neuropores can result in neural tube defects such as anencephaly or spina bifida. The dorsal part of the neural tube contains the alar plate, which is associated primarily with sensation. The ventral part of the neural tube contains the basal plate, which is primarily associated with motor (i.e., muscle) control.