Banks, savings banks, trust companies, insurance companies and other financial institutions and executors, administrators, guardians, committees, conservators and other fiduciaries subject to the laws of this State may invest their funds and the moneys in their custody or possession, available for investment, (a) in mortgages insured by the Federal Housing Administrator, including bonds secured by a mortgage so insured, (b) in debentures issued by said administrator and (c) in securities issued by national mortgage associations.