lOO 



COMPARATIVE MORPHOLOGY OF VERTEBRATES 



ICHTiiYOSAURS have a short temporal region, but elongate nasals and pre- 

 maxillaries form a long rostrum. There is a large supratemporal fossa and 

 enormous orbits, bounded above by pre- and postfrontals, below by an elongate 

 zygomatic, and containing a sclerotic ring. The nares are just in front of the 



Fig. 103. — Dorsal {A), posterior (B), ventral (C), and lateral (D) views of the skull 

 of Ichthyosaurus longijrons, after Woodward, nar, naris; pas, parasphenoid; pmx, 

 premaxiila; ptf, postfrontal; pto, postorbital, an, angular; art, articulare; bo, basioc- 

 cipital; bs, basisphenoid; eo, exoccipital ; /, frontal; j, zygomatic (jugal); /, Ic, lacrimal; 

 nU, maxillary; n, na nasal; nar, naris; oc, occipital condyle; 00, opisthotic; p, parietal; 

 pas, parasphenoid; pi, palatine; pmx, premaxillary; prf, psf, prefrontal; pt, pterygoid; 

 ptf, postfrontal; pto, postorbital; q, quadrate; qj, quadratojugal; sa, surangular; scl, 

 sclerotics; spl, splenial; spt, supratemporal; sq, squamosal; st, supratemporal. 



orbits and the parietal foramen is at the junction of frontals and parietals. All 

 four occipitalia bound the foramen magnum; the basisphenoid is short, the 

 presphenoid long; and the pterygoids are separated in front by the vomers, 

 leaving large pterygoid vacuities. The choanae are far forward. Teeth (some- 



FiG. 104. — Side and posterior views of skull of young Sphenodon, after Howes and 

 Swinnerton. Compare with fig. 76. Cartilage dotted; a, dentary; ar, articulate; 

 bo, basioccipital; cr, coronoid; eo, exoccipital; ep, epipterygoid; ex, extranasal; /, 

 frontal; h, hyoid; j, (jugal) zygomatic; mx, maxillary; n, nasal; 00, opisthotic; 

 p, parietal; pf, prefrontal; pm, premaxillary; poj, postfrontal; poo, postorbitjd; q, quad- 

 rate; qj, quadratojugal; so, supraoccipital; sq, squamosal. 



times absent) occur in grooves. The lower jaw has five or six distinct bones, 

 and a rib-lil^e hyoid has been found in some species. 



The only living Rhynchocephalian is Sphenodon {Hatleria) of New Zea- 

 land. It is lizard-like, but its skull (figs. 76, 104) differs in the three temporal 



