Sermo, a social net for doctors, has raised $26.7 million in a third funding round. Legg Mason Capital Management led the round and was joined by previous backers Longworth Venture Partners and Softbank Capital. The Cambridge, MA-based community site raised $3 million in a first round funding last September and $9.5 million in a second round in January. Sermo (the name is Latin for “conversation”) recently signed agreements with the U.S. Food and Drug Administration and American Medical Association to share information with and from its members. Release