The vertebrate head-segmented or a single morphogenetic structure?

A brief historical review of the discussion and evidence for a segmented head is given. The idea that the head is made up of a number of segments is accepted, and the number of segments is identified as five and one-half. The half is due to the fact that the sclerotomie segments alternate with myotomic ones. If the head is segmented, then structures can be assigned to segments. Several figures and a table summarize these assignments. A segmented head is viewed as part of the hypothesis that the vertebrate arose from a cephalochordate-like ancestor lacking a complex pharynx and having a better developed head.