The mdl file format is a container file , and it contains different files in this part, I’ll explain what file you can find in mdl container.
SMD Reference File (contain the geometry and bones hierarchy)
SMD Sequence File (contain all bone keyframe sequence, for motion models)
SMD Physic File (reference for collision model)
VTA File vertex animation (morphs map/facials animations)
Materials (VMT file)
Textures maps (VTF file)