ANATOMY OP VERTEBRATES. 



193 



123 



chanter better developed than in modern lizards: examples of 

 this bone four feet in length have been discovered. In the 

 almost equally colossal Sclelidosaur the toes 

 of the hind foot were reduced to four in num- 

 ber by suppression, as in the Crocodile, of 

 the fifth. In the Iguanodon they were re- 

 duced to three by the suppression also of the 

 first toe ; the retained toes were short and 

 broad, with phalanges in number respectively 

 three, four, and five ; but the latter so much 

 shorter as to reduce the outer to the same 

 length as the inner toe, and with the middle 

 one both longer and larger ; showing in the 

 great herbivorous Saurian an interesting ana- 

 logy to the hind limb of the Rhinoceros. 1 



§ 43. Dermosheleton of Fishes. — The scales 

 of fishes may be regarded, from their seat and 

 mode of developement, as parts of the dermo- 

 skeleton : and in the palaso- and meso-zoic 

 species they were ossified, in the form of 

 granules, tubercles, plates, or imbricated 

 scales. Bony fishes, with scales so soft and 

 soluble as to leave no trace in fossilization, 

 seem not to have existed before the creta- 

 ceous period : for even the exoskeleton of the 

 Leptolepidce of the lower and middle oolites 

 has been preserved to us through the thin coating of petrifiable 

 ganoine with which their minute and delicate scales were covered. 

 Tubercular integument, like the ' shagreen ' of sharks and dog- 

 fishes, has come down to us from a period as remote as the 

 Silurian. In skates and rays the skin is studded by bone in larger 

 masses ; sometimes, as in the ' Thornback,' developing a small 

 bent spine. 



The hard-rays in the fin of the Perch and other Acanthopteri, 

 the larger and fewer spear-like weapons of the Sticklebacks 

 (Gasterostei), Sheat-fishes (Siluridce), Trigger-fishes (Balistes), and 

 some Snipe-fishes ( Centriscus), are all parts of the dermoskeleton. 



In Balistes capriscus — a rare British fish — the anterior dorsal 

 is preceded by a strong erectile spine : its base is expanded and 

 perforated, and a bony bolt from the supporting plate passes freely 

 through it : when the spine is raised, a hollow at the back part of 



Bones of the leg and foot, 

 Chameleon, cli. 



VOL. I. 



CLIV. 



O 



