Schultze Hans-Peter, Arratia Gloria
Museum of Natural History and Department of Systematics and Ecology, The University of Kansas, Lawrence, Kansas 66045-2454.
J Morphol. 1986 Nov;190(2):215-241. doi: 10.1002/jmor.1051900206.
The centra of Lepisosteus are perichondral ossifications of arcualia (i.e., arcocentra), whereas those of Amia are direct perichordal ossifications (i.e., autocentra) that enclose the arcualia. The preural centra of Lepisosteus are monospondylous, whereas the ural centra are formations of inter- and basidorsal arcualia. In contrast, the preural centra of Amia are diplospondylous, whereas preural centrum 1 (and sometimes preural centrum 2) and ural centra are monospondylous. The ural centra of Lepisosteus are expansions of dorsal arcualia, but those of Amia are expansions of the basiventral autocentrum. This explains the fusion of the neural arches with the ural centra and the presence of autogenous hypurals in Lepisosteus, in contrast to the situation in Amia in which the compound ural neural arch (the fused ural neural arches) is free, and the hypurals are fused to the ural centra. Lepisosteus possesses true epurals, which are modified neural spines, whereas in Amia the "epurals" are positioned between the neural spines like radials. Lepisosteus and Amia possess a polyural caudal skeleton with a one-to-one relationship between ural centra and hypurals; the number of hypurals may be reduced in adult Lepisosteus.
雀鳝的椎体是弧片（即弧椎体）的软骨周骨化，而弓鳍鱼的椎体是直接的脊索周骨化（即自椎体），其包围着弧片。雀鳝的前尾椎体是单椎体的，而尾椎体是椎间弧片和背侧弧片的结构。相反，弓鳍鱼的前尾椎体是双椎体的，而第一前尾椎体（有时还有第二前尾椎体）和尾椎体是单椎体的。雀鳝的尾椎体是背侧弧片的扩展，但弓鳍鱼的尾椎体是腹侧自椎体的扩展。这解释了雀鳝中神经弓与尾椎体的融合以及自体尾下骨的存在，与之形成对比的是弓鳍鱼的情况，其中复合尾神经弓（融合的尾神经弓）是游离的，且尾下骨与尾椎体融合。雀鳝具有真正的上尾骨，它们是经过改造的神经棘，而在弓鳍鱼中，“上尾骨”像桡骨一样位于神经棘之间。雀鳝和弓鳍鱼都具有多尾尾骨骼，尾椎体和尾下骨之间存在一对一的关系；成年雀鳝的尾下骨数量可能会减少。
