92 COMPARATIVE MORPHOLOGY OF VERTEBRATES. 



jaw the bones are often fused, the two halves being united. Again the bones may 

 be distinct, the splenial being the least constant element. The hyoid apparatus 

 consists of a cartilaginous copula and two pairs of cornua which do not reach the 

 cranium. 



ICHTHYOSAURS have a short temporal region but elongate nasals and pre-max- 

 illaries form a long rostrum. There is a large supratemporal fossa and enor- 



D 



FIG. 94. Dorsal (A), posterior (B), ventral (C), and lateral (D) views of the skull 

 of Ichthyosaurus longifrons, after Woodward, nar, naris; pas, parasphenoid; pmx, pre 

 maxilla; ptf, postfrontal; pto, postorbital. Other letters as in fig. 68. 



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

 and containing a sclerotic ring. The nares are just in front of the 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 vacui- 



FlG. 95. Side and posterior views of skull of young Sphenodon, after Howes and Svvinner- 

 ton. Compare with fig. 69. Cartilage dotted; letters as in fig. 68. 



ties. The choanae are far forward. Teeth (sometimes absent) occur in grooves. 

 The lower jaw has five or six distinct bones, and a rib-like 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. 68, 95) differs in the three temporal 

 fossae, the infratemporal arcade being osseous as in no lizard. Then the quadrate 

 is anchylosed to pterygoid, squamosal and quadratojugal. Premaxillae, maxillae and 



