Neocortex has six layers, and just how prominent each layer is varies according to the cortical area or function. The innermost layer, layer 6, is prominent in the Nissl figure just near the '3b' label, and again in the region labeled '2'. Layer 5 is prominent in primary motor cortex because it contains some relatively large neuronal somata. The large layer 5 neurons in motor cortex in fact, are the largest neurons in the brain. Pyramidal cells are the principal neurons of the neocortex, the projection neurons.
Stellate cells are the local circuit neurons.
For the primary motor cortex, the pyramidal axons project directly to terminate in spinal motor centers controlling the distal muscles of the leg and particularly the arm. These axons can be a meter or more long, and a large cell body seems to be required to support such a long axon. This makes some sense if you consider that sensory cortex is specialized for input, whereas motor cortex is specialized for output. Layer 4 is the input layer. The axons coming in terminate in layer 4.