At the centre of the macula is the foveal pit where the cones are narrow and long, and, arranged in a hexagonal mosaic, the most dense, in contradistinction to the much fatter cones located more peripherally in the retina. At the foveal pit the other retinal layers are displaced, before building up along the foveal slope until the rim of the fovea, or parafovea, is reached, which is the thickest portion of the retina. The macula has a yellow pigmentation, from screening pigments, and is known as the macula lutea. The area directly surrounding the fovea has the highest density of rods converging on single bipolar cells. Since its cones have a much lesser convergence of signals, the fovea allows for the sharpest vision the eye can attain.Though the rod and cones are a mosaic of sorts, transmission from receptors, to bipolars, to ganglion cells is not direct. Since there are about 150 million receptors and only 1 million optic nerve fibres, there must be convergence and thus mixing of signals. Moreover, the horizontal action of the horizontal and amacrine cells can allow one area of the retina to control another (e.g. one stimulus inhibiting another). This inhibition is key to lessening the sum of messages sent to the higher regions of the brain. In some lower vertebrates (e.g. the pigeon), there is a "centrifugal" control of messages – that is, one layer can control another, or higher regions of the brain can drive the retinal nerve cells, but in primates this does not occur.
Bladder exstrophy  is a congenital anomaly that exists along the spectrum of the exstrophy-epispadias complex, and most notably involves protrusion of the urinary bladder through a defect in the abdominal wall. Its presentation is variable, often including abnormalities of the bony pelvis, pelvic floor, and genitalia. The underlying embryologic mechanism leading to bladder exstrophy is unknown, though it is thought to be in part due to failed reinforcement of the cloacal membrane by underlying mesoderm. Exstrophy means the inversion of a hollow organ. Signs and symptoms
The classic manifestation of bladder exstrophy presents with:
A defect in the abdominal wall occupied by both the exstrophied bladder as well as a portion of the urethra
A flattened puborectal sling
Separation of the pubic symphysis
Shortening of a pubic rami
External rotation of the pelvis.Females frequently have a displaced and narrowed  vaginal orifice, a bifid clitoris, and divergent labia. Cause
The cause is not yet clinically established but is thought to be in part due to failed reinforcement of the cloacal membrane by underlying mesoderm. Diagnosis
In a small retrospective study of 25 pregnancies five factors were found to be strongly associated with a prenatal diagnosis of bladder exstrophy:
Inability to visualize the bladder on ultrasound
A lower abdominal bulge
A small penis with anteriorly displaced scrotum
A low set umbilical insertion
Abnormal widening of the iliac crestsWhile a diagnosis of bladder exstrophy was made retrospectively in a majority of pregnancies, in only three cases was a prenatal diagnosis made.