ANATOMY OF VERTEBRATES. 



37 



31 



a communicating 



32 



up the hollow outside the cones, as Indicated by the dotted 

 tract in the section, fig. 27. But, in some, 

 aperture is left between the 

 terminal cones, as indicated 

 by the dotted line in fig. 31. 

 In many fishes the plates 

 by winch the bone attains 

 the periphery of the centrum 

 leave interspaces permanent- 

 ly occupied by cartilage, 

 forming cavities in the dried 

 or fossil bone, or giving a 



Abdominal vertebra (MugU) 



Abdominal vertebra, 



Pike (Esox) 



reticulate surface to the sides 

 of the centrum. The bases of the neur- and par-apophyses 

 sometimes expand so as to wholly inclose the centrum before 

 coalescing therewith ; as, for example, in the Tunny, where 

 the line of demarcation may be seen at the border of the articu- 

 lar concavity. 



In the Pike the neurapophyses seldom, in the Polyptcrus and 

 Amia, never, coalesce with the centrum : the letter s shows the 

 neurapophysial suture in fig. 32. In the Salmonidce the neur- 

 apophyses remain distinct from both the centrum and from each 

 other, in the anterior vertebra} ; where each developes a long and 

 slender spine. 1 The parapophyses remain for some time distinct 

 from the body of the vertebra, as well as from the ribs. In the 

 anterior vertebra? of the Carp the neurapophyses remain distinct, 

 as they do in the atlas of many other fishes, and a suture is ob- 

 servable between the parapophyses and centrum in embryo Cypri- 

 noids. In each vertebra the summits of the two neurapophyses 

 usually become anchylosed together, and to their spine ; but in the 

 Lepidosiren, fig. 41, the spine retains its character as a distinct 

 element, and is always attached by ligament to the top of the 

 neurapophysis, as it is in the Sturgeon, fig. 25. In the anterior 

 abdominal vertebra? of the Tetrodon, each of the neurapophyses, 

 though they coalesce in the interspace of the two spines to form 

 the roof of the neural canal, sends up its own broad truncated 

 spine ; and these are not much-developed oblique processes, but 

 gradually approximate and blend together, to form the single 

 normal spine at the fifth abdominal vertebra. 2 In the Barbel 

 the neural arches also support two spines, but one is placed 

 behind the other. 



1 xliv. vol. i. p. 16, No. 46. 



2 lb. vol. i. p. 81. 



