. Elements of Comparative Anatomy. 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). Th
. Elements of Comparative Anatomy. 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. 0 Occipital Condyle. Pa Parietal. P/Postfrontal. 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
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