154 



VERTEBRATE SKELETON 



(concha) to support the olfactory membrane, and in the tloor is a paraseptal 

 cartilage, parallel to the nasal septum, which lies below the vomero-nasal organ. 

 The pterygoquadrate consists of a pterygoid part and an epipterygoid process, 

 the quadrate chondrifying separately, there rarely being a connexion between the 

 two. Meckel's cartilage has a strong retroarticular part projecting behind 

 the articulation of the jaws. The hyobranchial apparatus consists of hyoid and 

 two branchial arches. The hyoid furnishes the columellar structures which arise 

 as a continuum and later form two cartilages, the etc- and hyostapes of Hoflf- 

 mann. Then the otostapes divides, the part adjoining the vestibular fenestra 

 forming the adult stapes, the rest and the hyostapes giving rise to the columella. 

 The branchial arches join the hyoid body, and vary greatly in detail in different 

 genera. The homology of the entoglossal process is uncertain. 



Lacertilia. — The lizard skull is primitive in some respects. No 

 farther reference to the chondrocranium is necessary save to say 

 that a considerable part of the cartilage persists through life, more in 



chameleons than in others. Some 

 lizards have incomplete ossification 

 of the parietals, leaving fontanelles 

 in the roof (Steliio, Sceloporus, etc.). 

 The ahsphenoid never ossifies, and in 

 the adult fused bones, sometimes of 

 diverse origin, are common. The 

 cartilage bones are mostly in the 

 occipital and otic regions, with some 

 in the orbital. All four occipitaha 

 are present (fig. 163), the supraoc- 

 cipital frequently extending over the 

 otic capsule; the occipital condyle is 

 entirely basioccipital. Pro- and opisthotic arise separately, the 

 latter fusing early with the exoccipital to an otoccipital bone, the 

 opisthotic furnishing the parotic process, which sometimes extends 

 laterally to articulate with the quadrate. The basisphenoid has a 

 well-marked sellar crest on its anterior internal margin, while the 

 parasphenoid fuses early with the bone. The cartilage bar of the 

 orbital region develops the orbitosphenoid, and in old individuals 

 occipitals and sphenoid fuse to a basal bone. There is little ossifica- 

 tion of the interorbital septum. 



The membrane bones are numerous at first, including parietals, 

 frontals, nasals, premaxillas, maxillas, pre- and postfrontals, zygo- 

 matics, lacrimals and squamosals on the dorsal surface; on the ventral 



Fig. 163. — Base of cranium of 

 Varanus. bo, basioccipital; bs, basis- 

 phenoid; eo, exoccipital; pa, parietal; 

 po, postorbital; pi, pterygoid; q, quad- 

 rate; s, squamosal; so, supraoccipital. 



