  Using an approximation method for eigenvalue distribution functions, we study
the temperature dependence of specific heat of the antiferromagnetic Heisenberg
model on the asymmetric railroad-trestle lattice. This model contains both the
sawtooth-lattice and Majumdar-Ghosh models as special cases. Making
extrapolations to the thermodynamic limit using finite size data up to 28
spins, it is found that specific heat of the Majumdar-Ghosh model has a
two-peak structure in its temperature dependence and those of systems near the
sawtooth-lattice point have a three-peak structure.
