THE LACERTILIA. 



101 



PmiB 



ard one another in the middle line, and so form a posterioi 

 nasal passage, partially separated from the oral cavity. 



The two rami of the lower jaw are 

 usually, though not invariably, firmly con- 

 nected at the symphysis — and each is 

 composed of five ossifications in addition 

 to the articulare. 



The hyoidean apparatus consists of an 

 elongated median rod, the anterior part 

 of which supports the base of the" tongue ; 

 and, usually, of two long cornua on each 

 side of this. The cephalic ends of the an- 

 terior comua may be perfectly free, and 

 lie upon the sides of the neck, as in Psam- 

 mosaurus ; or they may be traceable to, 

 and be connected with, the stapes and 

 the parotic processes, as in Sphenodon. 



The limbs may be completely devel- 

 oped ; or only one pair (either the ante- 

 rior or the posterior) may be present ; 

 or they may be entirely absent. When 

 present, they may be mere styliform rudi- 

 ments, or may possess any number of 'bo\ 

 digits from two to five. Even when the 

 limbs are altogether ^.bsent, the pectoral 

 arch remains, though the pelvic arch kg. to. 

 seems to vanish. When the pectoral arch 

 is complete, it consists of a suprascapula, 

 scapula, coracoid (with precoracoid and epicoracoid elements), 

 and two clavicles, united by an interclavicle, which lies in a 

 groove of the sternum. (Figs. 12 and 13, pp. 35 and 36.) 



The coracoids articulate with grooves in the anterolateral 

 edges of the sternum, and usually more or less cross and over- 

 lap one another, in front. 



In the genus JAalis, in which not a trace of a fore-limb is 

 discernible, there is a small sternum, consisting of a flat, 

 somewhat pentagonal, plate of cartilage, in which there is a 

 little coarsely-granular calcareous deposit; but this sternum 

 is connected with no ribs, nor, though it lies between the 

 coracoids, does it articulate with them. Each ooraco-scapulax 

 arch is a continuous cartilage, narrow in the middle, but ex- 

 panded at its dorsal, and still more at its sternal end, where 

 the right overlaps the left, and both are connected by fibrous 

 tissue with the sternum. The narrow middle part of the cora- 



Under-view of th« 

 skull of Oydodus: N-, 

 posterior nafial aperture. 



