54 MODIFICATIONS OF THE CAUDAL VEKTEBR.E. 



Fig. 10. 



the segments; these elements 

 consist of the centrum, the neu- 

 rapophyses, and neural spines, 

 the pleurapophyses, and the 

 parapophyses. In most fishes 

 the neural spines are connate 

 with the neurapophyses, and 

 these become confluent with 

 the centrums in most of the 

 segments ; the neurapophyses 

 are perforated directly by the 

 s^^inal nerves in many fishes, 

 as at nn (Fig. 8); they usually 

 develop anterior zygapophyses, 

 Z (Fig. 9). The centrums are 

 biconcave in all fishes, save the 

 lepidosteus, in which they are 

 convex in front, and concave 

 behind. The pleurapophyses, 

 pi (Fig. 9), form what are called 

 " false ribs," or free or " floating 

 ribs," in Anthropotomy ; they 

 articulate with the centrums in 

 the anterior trunk-vertebrse, 

 and then with the parapophy- 

 ses, p, which are usually con- 

 fluent with the centrum. The 

 parapophyses elongate, bend 

 down, and unite together at or 

 near to the end of the abdo- 

 men, and so form the contract- 

 ed hasmal canal, for the caudal 

 vessels, in the long and mus- 



