Chordate of the three subdivisions of chordates, all have distinct skulls. They include the hagfish, which have no vertebrae. Michael J. Benton commented that "craniates are characterized by their heads, just as chordates, or possibly all deuterostomes, are by their tails". Most craniates are vertebrates, in which the notochord is replaced by the vertebral column. These consist of a series of bony or cartilaginous cylindrical vertebrae, generally with neural arches that protect the spinal cord, and with projections that link the vertebrae. However hagfish have incomplete braincases and no vertebrae, and are therefore not regarded as vertebrates, but as members of
An Introduction to Animals and Political Theory normative political theory asking to what extent animals should be included in the domain of justice. States can and do regulate human-animal relationships, whether the animals in question are used in agriculture, as companions, or in some other way. Cochrane's focus is not on why laws are passed or on comparing laws, but in exploring what kind of laws "should" be passed. As his focus is on political theory, he is less concerned with questions about individual moral obligations than he is with institutional arrangements. He notes, however, that questions about animals have been neglected in political theory. In the