injury, which is not enough to restore function of cardiac muscle. However, this may be an important target for regenerative medicine as it implies that regeneration of cardiomyocytes, and consequently of myocardium, can be induced. Another example of reparative regeneration in humans is fingertip regeneration, which occurs after phalange amputation distal to the nail bed (especially in children) and rib regeneration, which occurs following osteotomy for scoliosis treatment (though usually regeneration is only partial and may take up to one year). Yet another example of regeneration in humans is vas deferens regeneration, which occurs after a vasectomy and which results in vasectomy failure. Reptiles The ability and degree of regeneration in reptiles differs among the various species, but the most notable and well-studied occurrence is tail-regeneration in lizards. In addition to lizards, regeneration has been observed in the tails and maxillary bone of crocodiles and adult neurogenesis has also been noted. Tail regeneration has never been observed in snakes. Lizards possess the highest regenerative capacity as a group. Following autotomous tail loss, epimorphic regeneration of a new tail proceeds through a blastema-mediated process that results in a functionally and morphologically similar structure. Chondrichthyes It has been estimated that the average shark loses about 30,000 to 40,000 teeth in a lifetime. Leopard sharks routinely replace their teeth every 9–12 days and this is an example of physiological regeneration. This can occur because shark teeth are not attached to a bone, but instead are developed within a bony cavity. Rhodopsin regeneration has been studied in skates and rays. After complete photo-bleaching, rhodopsin can completely regenerate within 2 hours in the retina. White bamboo sharks can regenerate at least two-thirds of their liver and this has been linked to three micro RNAs, xtr-miR-125b, fru-miR-204, and has-miR-142-3p_R-. In one study, two-thirds of the liver was removed and within 24 hours more than half of the liver had undergone hypertrophy. Some sharks can regenerate scales and even skin following damage. Within two weeks of skin wounding, mucus is secreted into the wound and this initiates the healing process. One study showed that the majority of the wounded area was regenerated within 4 months, but the regenerated area also showed a high degree of variability. See also Autotomy Regenerative medicine Neuroregeneration Epimorphosis Morphallaxis Polyphyodont Notes Sources Further reading Kevin Strange and Viravuth Yin, "A Shot at Regeneration: A once abandoned drug compound shows an ability to