CHORDATA 



oldest of reptilian types; usually regarded as ancestral to all the orders yet to 

 be mentioned. The only living species, Sphenodon piuictata, belongs to New 

 Zealand. 



Order VI. Dinosauria. 



This Mesozoic order included some of the largest land animals which have 

 ever existed. Some were from forty to one hundred feet long and twelve to 

 (\ventv feet high (Amphiccelias, Camarasaurus). In some there was an exo- 

 skelcton, some of the plates of which in the stegosaurs measured a yard across. 

 Among the characters are the fixed quadrate, jugal and postorbital arches, 

 three to ten sacral vertebrae, and ilium elongate in front of and behind the 

 aeetubulum. Some (Orthopoda) in pneumaticity of bones, in having the pubic 

 1 1. .lies directed backwards, and in the formation of an intratarsal joint, resembled 

 the birds, and have been regarded as the ancestors of that group. 



Order VII. Squamata (Lepidosauria, Plagiotremata). 



One of the characters which unite lizards and snakes and which has 

 given the name Plagiotremata is the transverse cloacal opening (fig. 577), 

 behind which, in the male, are the paired copulatory organs, each lying 

 in a sac from which they can be everted like the finger of a glove. The 

 names Squamata and Lepidosauria refer to the scaly condition of the 

 skin. The corium forms flattened papillae which resemble the scales of 

 fishes in that in many species they contain bony plates (fig. 509). Since 



an* 



ar 



FIG. 577. FIG. 578. 



TIG. 577. Hinder trunk and hind limbs of a lizard (from Ludwig-Leunis). a, 

 cloacal slit; b, femoral pores; sea, anal shield. 



I CG. 578.- Skull of Ameiva vulgar is. an, angulare; ar, articulare; co, epipterygoid ; 

 er, coronoid; </, dentary; fr, frontal; j, jugal; la, lacrimal; m, maxillary; na, nasal; p, 

 postorliital, above and behind it the parietal; pf, pref rental; pr, premaxilla; pt, ptery- 

 goid; q, quadrate; qj, quadratojugal; sq, squamosal; tr, transversum. 



the stratum corneum is thick on the top of the papillae and thinner between 

 them, rhomboid and oval plates occur, which either lie flush with each 

 other (shields) or overlap like shingles (scales). The rule is that the 

 head is covered with regularly arranged shields, each with its name, the 

 trunk with scales in longitudinal, transverse, and oblique lines. Outside 

 these is a layer of cornified cells, the pseudocuticula, and outside of all an 



