g2 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. 
IcatHyosaurs have a short temporal region but elongate nasals and pre-max- 
illaries form a long rostrum. There is a large supratemporal fossa and enor- 
Fic. 94.—Dorsal (A), posterior (B), ventral (C), and lateral (D) views of the skull 
of Ichthyosaurus longifrons, after Woodward. mar, naris; pas, parasphenoid; pmx, pre 
maxilla; ptf, postfrontal; pfo, 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- 
Fic. 95.—Side and posterior views of skull of young Sphenodon, after Howes and Swinner- 
ton. Compare with fig. 69. Cartilage dotted; letters as in fig. 68. 
ties. The choanz 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 (Hatteria) of New Zea- 
land. It is lizard-like, but its skull (figs. 68, 95) differs in the three temporal 
fosse, the infratemporal arcade being osseous as in no lizard. Then the quadrate 
is anchylosed to pterygoid, squamosal and quadratojugal. Premaxille, maxille and 
