l62 



VERTEBRATE SKELETON 



by a continuous copula with the two reduced branchial arches, the first of which 

 becomes the posterior cornu of the adult. 



The adult skull (tig. 173) has three temporal fossae, the lower 

 arcade consisting of squamosal, quadratojugal and zygomatic, the 

 upper of postorbital and squamosal, while an arcade, a process of 

 the squamosal which extends to the parietal, separates the superior 

 fossa from the posterior. The large orbit is bounded by prefrontal, 

 maxilla, zygomatic, postorbital, postfrontal and frontal, there being 

 no lacrimal. The parietal foramen is between the narrow parietals 

 which form nearly the whole of the roof of the brain case. The 



Fig. 173. — Side and basal views of cranium of young Sphenodon (Howes and 

 Swinnerton, 'oi). Cartilage stippled, a, dentale; ar, articulate; bo, basioccipital; cr, 

 coronoid; eo, exoccipital; ep, epipterygoid; ex, extranasal; /, frontal; h, hyoid;j, zygo- 

 matic; mx, maxilla; n, nasal; oo, opisthotic; p, parietal; pf, prefrontal; pm, premaxilla; 

 pof, postfrontal; poo, postorbital; q, quadrate; qj, quadratojugal; so, supraoccipital; 

 sq, squamosal. 



separate nares are almost terminal. The pterygoids (fig. 174), 

 which have a basipterygoid articulation with the basisphenoid, 

 extend forwards to the vomers and separate the palatines of the two 

 sides. A transversum is present and the epipterygoid extends to 

 the parietal. Both squamosal and quadratojugal fix the quadrate, 

 the quadratojugal being forced ventrally by the long posterior proc- 

 ess of the zygomatic which connects with the squamosal. Dentale, 

 splenial, coronoid, angulare and surangulare are separate in the adult. 

 The hyoid apparatus has a body and two pairs of cornua, the anterior 

 (hyoid) persisting as cartilage connected with the stapes through 

 life. The posterior cornua are ossified except at the tips. 



A number of fossil genera, once included in the Rhynchocephala, have been 

 transferred to other orders, but, as little is known of the skulls of these, they 

 may be grouped here. All are diapsidan, so far as known, the fossa; being large 

 in PalceohaUeria (fig. 175) and Champosaurus, the latter genus, like Saitraiwdon 

 and Rhynchosaurus, lacking a parietal foramen; it also had a snout elongate as in 

 Gavials. Procolophon (fig. 78), which is near the ancestors of the Rhynchoce- 



