ANATOMY OF VERTEBRATES, 



107 



cuirass. In the composition of tlii 

 sntures, not mncons grooves, may be 

 discerned the i'ollowing lAutesi : 5, 

 n/fdum ; 6, lateral ; 7, jjremedian ; 8, 

 jirelateral; 9, rostral; \2,dorsomedian; 

 14, ]>ostdorsoinediun ; is, suhlatcral; 20, 

 liostventrolateral; 22, preventrolateral ; 

 24, .sid)orhital. 



Tlie blanli space l)etween the neu- 

 ral, v., and haBmal, A, spines of the 

 fossil endoskeleton indicates the posi- 

 tion of the soft ' notochord,' c, which 

 has l:)cen dissolved away. 



In the Pterichtlnjs of the same geo- 

 logical formation, the helmet was 

 moveably articulated with the truidi- 

 buckler. 



In Cephalaftpis the armour of the 

 head was shield-shaped, with the pos- 

 terior angles produced backward in a 

 pointed form. 



The fishes with enamelled dermal 

 bones in the form of j^lates, whether 

 coarticulated, fig. 127, or detached as in 

 the Sheat-fishes and Sturgeons, fig. 125, 

 d J), d s, are called ' placoganoid : ' 

 those in which they have the size, 

 form, and overla2)ping arrangement of 

 scales, fig. 126, are called 'lepidoganoid.' 

 The genera Poh/ptcrns and Lcpidostcus 

 exceptionally exemplify the latter con- 

 dition of the dermoskeleton at the 

 ])resent day : it was the rule with the 

 fishes of the mesozoic period, and 

 with those of the pala30zoic wliich 

 were not ' placoid ' or 'placoganoid.' 



In fig. 126, « indicates the outer 

 siu-face of parts of two series of the 

 rhomboidal ganoid scales of the extinct 

 Amhlfjpterus: and h \\\e inner surface 

 of two scales, showing the ridge pro- 

 duced at one end into a projecting 

 jieg, which fits into a notch of the next 



s armour, as defined by 



127 



L 



'N 



'^:'S. 



: *l 



EiuTo-an(U\T -kelttoii, Coccr^s^jcs. clvt. 



