Each bony canal contains within it a membranous canal, at the end of which it is dilated to form an ampulla.
Swellings at the base of each canal, the ampullae, are visible.
First seven abdominal terga and sterna with densely and veryfinelyasperate ampullae, those of intermediate segments smaller, that of 7th tergum larger than the others.
This may seat them further inside the aortic ampulla, but may also deliver more loops into the pulmonary side of the duct.
The second coil was, therefore, implanted retrogradely with the catheter remaining in the ductal ampulla.
Coils were positioned insidetheductin the long tubular ducts or straddling the duct (with some loops in the pulmonary artery and some in the aortic ampulla).
The ductal ampulla was either absent or very small infivepatients, so we implanted a coil which had been cut short.
Fourthly, the coils can be placed even in patients with a relatively small ductal ampulla.
