:;L> mMl'AKATIVK ANATn.MY. 



the whole .skin, and which exhibit exactly the same structure as 

 the teeth proper, which will be described later. 



Such dermal ili'nt jclc- are found in the skin of Elasmobranchs, 

 Ganoids, Siluroids. and I )i pnoa us : the large shields, which, in 

 the armoured <!an<>idsand Siluroids (Fig. 19), Lophobranchii and 

 Plectognathi, heroine united to form a strong bony cuirass, may be 

 derived from tin- gradual i'usion of the above-mentioned basal- 

 plates to form bands and networks. One may even extend this 

 still further, and dcri\- phylogmet ically all the scales of Fishes, 

 as well as the investing bones of the pectoral arch (e.g. 

 Teleostei) and of the primordial skull in the same manner (cp. 

 Fig. 53). 1 



Fossil genera of Amphibia have bequeathed but slight traces 

 of this strong dermal armour to the existing forms of the group: 

 as examples may be mentioned the bony plates in the skin of the 

 back of certain Anura (Ceratophrys dorsata and Ephippifer auran- 

 tiacus), as well as the scales lying between the ring-like scutes of 

 the footless Amphibia (Gymnophiona) (comp. p. 20). The latter 

 maybe derived from such a scaly covering as that of the ancient 

 Salamander (Discosaurus) of the Carboniferous formation. 



The dermal skeleton of fossil Reptilian genera, as, for instance, 

 of many Ornithoscelida (Stegosaurus), was still more highly 

 developed. In these, enormous bony plates and spines, sometimes 

 as much as G'> centimetres long, were present in the dorsal region. 

 Teleosaurus also, as Avell as the Triassic Aetosaurus ferratus. 

 possessed a strong exoskeleton. Amongst existing Reptiles, the 

 Crocodiles, many Lizards (Anguis, Cyclodus, Scincus), and more 

 'specially the Chelonia, exhibit a well-developed dermal skeleton. 

 In the latter group a dorsal and ventral shield (carapace and 

 pla-troii) consisting of numerous pieces and completely enclosing 

 the body must be noticed. Both arise independently of the endo- 

 skeleton, which is preformed in cartilage, that is to say, they are true 

 exoskeletal membrane bones (cp. note on p. (>-) ; the exoskeletmi. 

 however, comes into the closest relation with the endoskeleton, and 

 may supplant it here and there : thus, in Testudo, for instance, the 

 thoracic ami lumbar vertem-;e and ril>s become quite rudimentan . 



Birds have no dermal skeleton, as already mentioned in the 

 chapter mi the integument. 



It is uncertain wheth'-r the dermal skeleton present in Arma- 

 dillos (Loricata) 1 only among .Maininals is to l>e derived <lirectly 



<lt-nn:il il'-nli'-li^ nf Elasmobranchs an- i.fifji sjM.kni nf as jilai'oid. and 

 tin' finnly-j'iiiit.-il M-ali-- i.r LepidosteoB and Poly pterus as ganoid M-alrs : Imiii an' 



riivrivl I'.v a layi'T "f i-iiaiiii'l |i|n!ia!']y ili-vi-lii|n-il iVdin tin' 'I'tii'lrvin, a!:>l thus Imtli 



epidermis and aenna take i>art in ihrir I'nnii.iiiiui. Smm- Kislics (..-/. Klc.'trir \i-.\\, 



Sjiatlllaiia. snlii'- I 



In Aniia.li!!.!- iln- .l.rinil .-K-.-l.-toii .-..n a scries of transverse l>ony 



BCUtM, wlii.-li a iv IIP i\ a Mr mi <nn- another, \\ lnl'- iii C 1 y |it i ill on, a fossil I iirTiil 'IT of 



to^-tlii- ' 



iliis Kroiiji. tin- i!> -rinal |.lai- - were linnly uniti-'l to^-tlii-r t I'ITIII .1 lar^' -lii'-M. 

 which I tli- \vh"I'- i 



