Neurological and osteological definitions of cervical vertebrae in mammals

The presence of seven cervical vertebrae is an almost universal mammalian trait. The posterior boundary of the cervical series is traditionally defined osteologically, but its location is also predictable using neurological markers of the brachial plexus. The existence of three living mammalian genera with osteologically defined cervical counts other than seven offers the opportunity to examine the coincidence of osteological and neurological definitions of the term 'cervical'. Despite variations in rib and articular processes of cervical vertebrae dissections of the brachial plexuses of these genera reveal that neurological and osteological markers of the cervical series define the same, nontraditional, posterior boundaries of the series. Subdivision of the predetermined cervical mesoderm into a nontraditional number of segments has not altered the relationship of the limb or its innervation to the cervical/thoracic boundary. This nontraditional subdivision appears to have evolved separately at least three times.