32 



ANATOMY OF VERTEBRATES. 



layer of the notochordal capsule has assumed the texture of tough 

 hyaline cartilage; and not only are firm opakc cartilaginous 

 neurapophyses present, but also parapophyses, pleurapophyses, 



Fore part of skeleton, Lamprey (Pctromyzon) 



and neural spines. The part of the iieurapophysis bounding the 

 true neural canal is usually distinct from that bounding the fat- 

 filled fissure above. The parapophyses are united by a con- 

 tinuous plate of cartilage forming an inverted arch beneath the 



aorta, in the trunk, ana- 

 logous to that formed by 

 bone in the lower neck- 

 vertebra of birds, fig. 20. 



iuterneural cartilage 



ueural spine 



filiro-adipose 

 canal 



neural canal 

 gelatinous chorda 



inner layer of 

 fibrous capsule as 

 hyaline cartilage 



O Pleurapophysis 



In the ChimcBra 

 der subossified 



ngs 



parapophysis 

 - interhitmal cartilage 



hanual canal 

 Abdominal vertebra, Sturgeon 



in the 



o 



nous sheath of the noto- 

 chord, which are more 

 numerous than the neu- 

 ral arches. These, where unconflueiit with each other, are 

 distinct also from the parapophyses, which in the tail bend 

 down to form the hoemal arches. In the Mediterranean Grey 

 Shark (Notidanus cinereus) the vertebral centres are still feebly 

 and irrelatively marked out by numerous slender rings of hard 

 cartilage in the notochordal capsule, the number of vertebra? being 

 more definitely indicated by the neurapophyses and parapophyses ; 

 but these remain cartilaginous. 



In the Lepidosiren the peripheral vertebral elements, fig. 41, ??, 

 ns, p, hs, are ossified, but the notochord, ch, with a thicker and 

 condensed capsule, remains. In the Piked Dog-fish (^Acanthias) 

 the vertebral centres coincide in number with the neural arches, 

 and are defined by a thin plate of bone, shaped like an hour- 

 glass, and forming the conical cavity at each end of the centrum : 

 the rest of which is cartilaginous external to the ' hour-glass,' and 

 subgelatinous within its terminal cavities. In the Spotted Dog- 

 fish (Scyllium) the two thin bony cones of each centrum are con- 



