DEVELOPMENT OF THE SKULL IN THE LACERTILIA. 
597 
in the middle-class Bird (Fowl, Goose, &c.), whereas the low Bird (the Ostrich and its 
relatives) does not show so high a condition, and the highest Birds (Crows, Songsters, 
and Parrots) abort these very parts, going beyond that degree of specialization. 
This corresponds with what I showed twelve years ago, namely, that the Struthious 
type of skull contained several Batrachian (sub-reptilian) characters : in height, 
zoologically, the high Lizard is in some respects on a level with the Fowl and the 
Goose—birds of the middle level. 
The skull of this normal Lizard has so many points of zoological and of morphological 
interest, that I shall, as I did in my paper on the “ Salmon’s Skull,” describe the adult 
condition first, and then go back to its primordial state, and trace it step by step 
upwards. 
The skull of the adult Lizard is a very compound piece of architecture, whether we 
consider the “ stones ” of the budding or its “ style it is a sort of accretion of all that 
has gone before it in the Vertebrate sub-kingdom. 
Hence, if I fad in giving a simple morphological solution of all its structural 
difficulties, I shall fail for want of knowledge of the structure and development of 
the Vertebrata that lie below the Lizards of this epoch, and of the Beptiles (generally) 
of this epoch. 
As to the members of the great Reptilian class, extinct and recent, of the latter 
much remains to be done, but they are within reach ; of the extinct forms, most of the 
shreds and patches of our knowledge of them relate to the dermo-skeleton merely. 
But the true opener of the eyes is the study of development , and the light lit by 
this method goes on increasing in its illuminating power, as type after type is set 
in light. 
Skull of Adidt Lizards. (Lacerta and Zootoca.) 
a. The investing hones. The epidermic scales and their matrix are both very thin ; 
only in the head and across the coracoids do dermal bones exist in Lacerta; in some 
kinds, as Cyclodus and Anguis, the scales of the body have “scutes” of bone beneath 
them. 
The cephalic “scutes” of Lacerta are ossifications of the inner part of the “cutis 
vera ” and of the subcutaneous stroma; they are composed of both these layers, and 
are scabrous where no muscle intervenes, but their sub-muscular tracts are smooth, and 
are subcutaneous in origin. 
Thus the ganoid layer is gone, and yet most of the splints of the head are true 
“ dermostoses ” or dermal scutes, and their proper counterparts may be traced down¬ 
wards through the lower forms of Reptiles, Amphibia (“ Labyrinthoclonts ”), and Ganoid 
Fishes. 
Some Lizards, as the “ Varanians” or Monitors, have their investing bones as much 
specialized as the Osseous Fishes on one hand, and the Birds on the other: Lacerta 
has a, very generalized bony roof to its skull. 
