Ultrasonic wave propagation in cortical medium is of interest for various biomedical purposes. As a matter of fact, wave-guiding of energy along bones of various geometry is nowadays a research field of interest with application to sensing and stimulation. Since performance level is subject to good understanding of the medium parameters (geometry, thickness, topology, density, viscoelasticity ?), the study intends to characterize the generation and propagation of guided waves in a known phantom bone. To limit the number of solutions, the present study focuses on low frequency propagation, where mode analysis is easier. In order to build an accurate numerical model, the material mechanical properties are first characterized. A 2.5D Semi-Analytical Finite Element (SAFE) method is then used to find dispersion curves and mode shapes in the cross section of the simulated bone at low frequency (~50kHz). A 3D FEM simulation is run to confirm the 2.5D simulation results and further assess the attenuation coefficient of the propagating guided modes. The simulated results are finally confronted to experimental measurements. A resin rib (a=6.5, b=3.5mm, L=220mm) is excited with a mechanical pulse produced by an attached PZT element and the 3D resulting displacements are measured along the bone surface and used as input data to a 2D FFT signal analysis to build the dispersion diagram.