Forelimb-related areas of the motor cortex communicate directly to downstream areas in the brainstem and spinal cord via axons that project to and through the pyramidal tract. To better understand the diversity of the brainstem branching patterns of these pyramidal tract projections, we used MAPseq, a molecular barcode technique for population-scale sampling with single-axon resolution. In experiments using mice of both sexes, we first confirmed prior results demonstrating the basic efficacy of axonal barcode identification of M1 pyramidal-tract type (PT) axons, including corticobulbar (CBULB) and corticospinal (CSPI) subclasses. We then used multiplexed MAPseq to analyze projections from M1 and M2 (caudal and rostral forelimb areas). The four basic axon subclasses comprising these projections (M1-CSPI, M1-CBULB, M2-CSPI, M2-CBULB) showed a complex mix of differences and similarities in their brainstem projection profiles. This included relatively abundant branching by all classes in the dorsal midbrain, b...