^82 STRUCTURE OF VERTEBRATES 



each of these is probably into four elements on each side, called 

 from above downwards, pharyngo-, epi-, cerato-, and hypo- 

 branchials, and a median ventral basibranchial. Fishes have 

 different variants on this plan ; that of the dogfish has been 

 described on p. 319. 



In bony fish the upper jaw cartilage ossifies to form at least 

 three bones, the autopalatine, the epipterygoid, and the quadrate ; 

 in primitive Crossopterygii there were several pterygoids. In 

 the tetrapods the anterior end of the cartilage does not ossify, 



_,-- pm 



pro. 

 col. 



Fig. 454. — The skull of the lizard Uromastix. 



A , Dorsal view ; B, ventral view. 



al.sp'., Cartilage representing alisphenoid ; b.oc, basioccipital ; b.sp., basisphenoid ; col., columella auris ; 

 epipt., epipterygoid ; ex.oc, exoccipital ; fr., frontal ; ju., jugal ; mx., maxilla ; n., nasal ; nas'., region 

 from which cartilaginous nasal capsule has been removed ; oc, occipital condyle ; orb., orbit ; par., 

 parietal ; pL, palatine ; pm., premaxilla ; prf., prefrontal and lacrimal, fused ; pro., pro-otic ; pt., 

 pterygoid ; ptf., postfrontal and postorbital, fused ; q., quadrate ; rs., rostrum ; s.oc, supraoccipital ; 

 s.t.f., supratemporal foramen ; sq., squamosal ; suL, supratemporal bone (very small) ; tpt., trans- 

 palatine ; v., vomer (' prevomer '). 



and the epipterygoid is the bone which in mammals is called 

 alisphenoid. In most vertebrates except mammals, the quadrate, 

 whether large as in snakes or small and unossified as in the frog, 

 is the part which articulates with the lower jaw ; in the mammals, 

 although present, it has been put to other uses which will be 

 described below. 



The upper jaw has various degrees and types of attachment 

 to the dorsal skull, which are classified into three main groups. 

 The simplest, although not necessarily the most primitive, is 

 known as hyostylic, and is found in most modern Chondrichthyes 

 (Fig. 455) and in all bony fish except the Dipnoi. Its characteristic 

 feature is that the chief or only connection between skull and 



