156 ANATOMY OF VERTEBRATES. 



goids : these bones are applied to the back part of the tympanic, 

 and the slender ' columella' rests upon the middle of their upper 

 surface. The parietal is perforated near its anterior border. 

 The postfrontal has a descending postorbital process. The pre- 

 frontal developes a partial post-lateral wall for the rhinencephalic 

 chamber ; externally it supports an antorbital dermal bone : the 

 small perforated lacrymal is a distinct bone. The nasal and pre- 

 maxillary are both single bones, as in most Lacertians. The 

 malar, wedged anteriorly between the maxillary, palatine, lacrymal 

 and ectopterygoid, curves backward as a slender style terminating 

 in a point, leaving the orbit uncircled by bone behind : the 

 squamosal, wedged behind between the mastoid and tympanic, 

 curves forward to a point beneath the postfrontal. 



In the American Monitor ( Tejus nigropunctatus) the nasals are 

 divided: the malar articulates behind with the postorbital — a dis- 

 memberment of the postfrontal, which continues the zygomatic 

 arch with the squamosal : there is no •' foramen parietale.' 



In the Chameleon the teeth are short, and so confluent with the 

 jaws that these appear to have simply a serrated margin. The 

 external nostrils perforate the maxillary bone ; a long, compressed, 

 serrated crest arches upward and backward from the superoccipital 

 and parietal bones, and joins the processes of bone continued from 

 the mastoids. In the Chameleo bifurcus the anterior fork-like 

 productions are formed by the maxillary and prefrontal bones. 

 The premaxillary at the bottom of the cleft is very small. 



In Draco volans there is merely the rudiment of a spine or 

 ridge from the superoccipital ; an arched transverse ridge separates 

 the occipital from the parietal region of the skull. The post- 

 frontal, mastoid, and paroccipital project successively from their 

 respective cranial segments, and well manifest their character as 

 the transverse processes of these. 



The vacuities in the bony palate are many, and show much 

 variety in the cold-blooded, especially the reptilian, series, in 

 regard to their number, kind, and relative size. The most con- 

 stant are those which are more or less circumscribed by the max- 

 illary and pterygoid, and constitute a pair. They are present in 

 Pohjpterus and most Ganoids, bounded outwardly by the maxil- 

 lary, medially by the palatine, and behind by the pterygoid. 

 In the Menopome the vomer, fig. 73, /, forms the median and 

 the pterygoid,/, the posterior boundary. In the Frog, fig. 98, 

 a, the pterygo-maxillary vacuities, y, are divided from each 

 other by the basisphenoid ; whilst the palatine forms the front 

 boundary and separates them from the nasal apertures, n. In 



