SKULL — REPTILES 



151 



All four occipitalia form the border of the foramen magnum and the basioccip- 

 ital alone bears the condyle. Lateral to the exoccipital is an opisthotic, sepa- 

 rate from the prootic. The quadrate is held by squamosal and quadratojugal, 

 and joins the pterygoid on the median side. This latter bone is long; the pair, 

 including a pterygoid vacuity between them, meet in front, separating palatines 

 and vomers of the two sides. Behind they rest against the basisphenoid. Os 

 transversum and epipterygoid are present. The basisphenoid is short, but 

 prolonged forwards by a rostrum, interpreted both as a pre- and a parasphenoid. 

 Teeth, when present, are confined to the margins of the jaw. In the lower jaw 

 dentale, angulare, surangulare and articulare are distinct. A stout rib-hke hyoid 

 occurs, but no other traces of visceral arches are known. 



A C 



Fig. 160. — Dorsal, basal, ventral and side views of skull of Ichthyosaurus (Wood- 

 ward, '98). an, angulare; art, articulare; bo, basioccipital; bs, basisphenoid; eo, exoc- 

 cipital; /, frontal; j, zygomatic; /, Ic, lacrimal; ml, maxilla; n, na, nasal; nar, naris; 

 oc, occipital condyle; p, pa, parietal; pas, parasphenoid; pi, palatine; pmx, premaxilla; 

 prf, psf, prefrontal; pt, pterygoid; ptf, postf rental; pto, postorbital; q, quadrate; qj, 

 quadratojugal; sa, surangulare; scl, sclerotics; spl, splenial; st, spt, supratemporal ; 

 sq, squamosal. 



SQUAMATA have an elongate skull with slender bones and, 

 except in a few lizards, a moveable quadrate, which lies in front of 

 the tympanic cavity. The lower temporal arcade is never complete, 

 and in most genera (snakes and some lizards excepted) the upper 

 arcade is formed by postfrontal and squamosal. Another squamosal 

 process (absent in Ophidia) may meet the parietal, limiting the large 

 posttemporal fossa. A parietal foramen is present, except in Ophi- 

 dia, and usually parietals, frontals and premaxillae of the two sides 

 are fused in the middle line. The nares are separate. Palatal proc- 

 esses of maxillae and premaxillae are weakly developed. The paired 

 vomers are always visible and the palatines may or may not meet in 

 the middle line. The pterygoid vacuity is large, the pterygoids 

 extending back to the quadrate and also articulating with a more or 



