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The median-ulnar anastomosis (Martin-Gruber) of the forearm was present in 15% of the normal fetuses dissected. Among the congenitally abnormal fetuses, all the cases of trisomy 21 had the anastomosis in both forearms. The anastomosis is usually between the anterior interosseous nerve and the ulnar nerve and could be classified into six basic patterns.
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Srinivasan et al. (1981) studied this question.
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