The dorsal root ganglion of the American alligator (Alligator mississippiensis).

The peripheral nervous system of vertebrates develops through the merger of neuritic outgrowths from the central nervous system, and derivatives of the neural crest cells (ncc), including the spinal (or dorsal root) ganglia. Before the neural crest cells differentiate into neural tissue, they migrate through the vertebrate embryo. Relatively little comparative work has been done on the potential relationship between differential ncc migration and interspecific variation in the spinal ganglia. In Alligator mississippiensis, the sensory ganglia are located on the dorsal root, immediately distal (lateral) to the bony margins of the intervertebral foramen. No clear evidence of afferent (sensory) nerves, equivalent to the sinuvertebral nerve of mammals, was observed within the vertebral canal of Alligator. The biomechanical influence, if any, between the large spinal venous sinus of Alligator and the sensory dorsal root ganglia remains unknown.