ABSTRACT
This chapter examines the comparative anatomy of the tetrapod spinal cord from the viewpoints of structure and evolution. Only the anatomy of dorsal root connections is considered; this is to evaluate whether morphological questions with implied evolutionary significance can be formulated and then experimentally tested. Direct dorsal root connections are present among the intranuclear dendritic segments of medial (axial) and lateral (limb) motor neurons. Before the spinal anatomy of lower tetrapods is considered, it may be well to discuss additional preliminary mammalian data on dorsal root connections that have been obtained in the horse and harbor seal. The increasing invasion and synaptic spread of dorsal root connections in the ventral horn of iguanids may reflect the better terrestrial adaptations and climbing abilities of these lizards compared with the principally amphibious adaptation of crocodilians. Afferent dorsal root connections appear limited to the distal ends of dorsal dendrites that project into the zona intermedia and dorsal horn.
