VERTEBRAL COLUMN OF FISHES. 



51 



Fara. Chimceroidel, Example, 



Edaphodontidce, 



Cliima3i"a. 



{Ediipliodon. 

 Passalodon. 



Ordo XI. — Plagiostomi. 



Endo-skeleton cartilaginous oi* partially ossified ; exo-skeleton pla- 

 coid ; gills fixed with five or more gill-apertures ; no swim-bladder ; 

 scapular arch detached from the head ; ventrals abdominal ; intestine 

 with spiral valve. Copula gaudent. 



Fam. HyhodontidcE, 

 CestraciontidcE, 

 Notodanidce, 

 SpinacidcE, 

 ScyUiidce, 

 Kictitantes, 

 Lamnidce, 

 Aloj)eciida', 

 Scymniida;, 

 Squatinoi, 

 ZygcenidcB, 

 PristidcB, 

 Rhinobatidce, 

 Torpedinidce, 

 RaiidcE, 

 TrygonidcE, 

 Myliohatidce, 

 Cephalopteridce, 



Example, Ilybodus. 

 Cestracion. 

 Gray-shark. 

 Piked Dog-fish. 

 Spotted Dog-fish. 

 Tope. 

 Porbeagle. 

 Fox-shark. 

 Greenland-shark. 

 Monk-fish. 

 Hammerhead-shark. 

 Saw-fish. 

 Rhinobates. 

 Electric-ray. 

 Ray or Skate. 

 Sting-ray or Fireflaire. 

 Eagle-ray. 

 Cephaloptera. 



Adipose substance. \ 



x^'^^A Neural canal. 



Inner laye 



Outer laye 

 of fibrous capsule. 



— Gelatinous chorda. 



Transverse vertical section of vertebral column of ilyxinc. 



In the Myxinoid fishes the neural and hajinal canals are formcid 

 by a sepai-ation of the layers of the outer division of the fibro-mem- 

 branous sheath of the gelatinous chorda (7?//. 10.) ; the neural canal 

 extending the whole length of the upper part of the chorda, the 

 ha3mal canal being confined to the caudal region, where it contains the 

 prolongation of the aorta and the vena cava (xxi. p. 25.). In the 

 Lamprey {Petromyzon) cartilaginous laminaj (,/?</. 11. n) are de- 

 veloped in the fibrous sheath (/), and give tlie first indication of neural 

 arches. "We should hardly expect to find the unity of the vertebral 



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