SKULL OF VEETEBKATA. 



459 



The covering bones are : the parietals, which are paired (Ohelonii 

 and Aves), or unpa,ired (Ophi- 

 diij Saurii, Crocodilini) (Fig. 

 248, Fa). The frontal also 

 is unpaired in most of the 

 Saurii, and in the Crocodilini 

 (Fig. 248, B Fr). It is paired 

 in Lacerta and Monitor (Fig, 

 248, A Fr), and in the Ophi- 

 dii, Chelonii, and Aves, In 

 the Reptilia the postfrontals 

 limit the posterior edge of 

 the orbit (Figs. 248, Pf; 249, 

 B G Pf), 



In the middle of the 

 ethmoidal region there is a 

 considerable remnant of the 

 primordial cranium (Chelonii). 

 The lateral ethmoids (pre- 

 frontals) bound the anterior 

 edge of the orbit in Reptiles ; 

 in Birds they appear to be 

 connected with the median 

 portion of the ethmoid. The 

 vomer is paired in the Ophidii 

 and Saurii (Fig. 250, Vo). The 

 nasals are almost always absent 

 from its upper surface in the 

 Chelonii, and in some of the 

 Saurii. A new covering bone 

 which is seen on the outer 



face of the ethmoidal capsule is the lachrymal ; it is found in most 

 Saurii^ Crocodilini, and Aves (Figs. 248, 249, L). 



Fig. 248. Skull of Eeptilia; seen from 

 above. A Monitor. B Crocodile. Os Snpra- 

 occipital. Occipital Condyle. Pa Parietal. 

 P/ Postf rontal. Fr Frontal. Pr/ Pre-frontal. 

 L Lachrymal. N Nasal. Sq Squamosal. 

 Qj Quadratojugal. Ju Jugal. Q Quadrate. 

 Mx Maxilla. Px Premaxilla. co Columella. 



§ 348. 



The anterior portion of the primitive palato-quadrate cartilage 

 undergoes ati'ophy very early, so that the bones which belong to it 

 are partly developed on the skull itself. The hinder portion of 

 the palato-quadi'ate persists as the quadi'ate (Fig. 249, Q). The 

 quadrate is movable in the Saurii, Ophidii, and Aves, while in 

 the Chelonii and Crocodilini it is firmly united to the skull. The 

 whole complex of bones, which is differentiated in the palato- 

 quadrate cartilage, is intimately and immovably connected with the 

 cranium, while, when the quadrate bone is movable, some, at least, 

 of these bones are also so. 



Another character is due to the development of the nasal 

 cavity (see also § 413). The bones, which in Fishes are placed 

 at the sides of the base of the skull, extend to the middle 



