The spinal cord of two tetraodontiform fishes, the Japanese file fish (Navodon 
modestus) and the panther puffer (Takifugu pardalis), are unusual among 
vertebrates in having a markedly abbreviated spinal cord with a long and 
flattened filum terminale. Only the rostral short part of the cord of both 
species is cylindrical; the greater part of the cord is markedly flat. The 
majority of the spinal nerve roots leave the short cylindrical part. The 
flattened part of the cord contains the central canal, myelinated nerve fibers, 
and a few motoneurons surrounding the cauda equina, and it is histologically 
similar to the filum terminale of amphibians and mammals. The spinal cords of 
other teleosts, the sun-fish and angler, also are abbreviated and possess a 
filum terminale and cauda equina. These orders possess an enormous head and 
short trunk. However, the correlation between this body form and an abbreviated 
cord is not causal, since the tetraodontiform species described here show 
ordinary body proportions. The spinal cord may be abbreviated in tetraodontiform 
fishes in general.