120 



AMPHIBIA 



CLASS II 



Fig. 20C. 



Dorsal aspect of the skull of Mtiuiierpeton pulcherrimwn, 

 PritscU. Restored, i/i (after Credrier). A, Orbit ; Piiix, 

 Premaxilla ; Mx, Maxilla ; Na, Nasal ; Prf, Prefrontal ; Fr, 

 Frontal ; Ptf, Postfrontal ; Pa, Parietal ; Por, Postorbital ; 

 X, Anterior ; Sq, Posterior squamosal ; Ep, Epiotic ; St, So, 

 Supratemporal ; Ju, Jugal. 



The thin, flat bones constituting the cranial roof are of dermal origin, as 

 in the case of cartilaginous G-anoids. The brain cavity is protected by the 



large, paired parietals, posterior to 

 which are two pairs of supra- 

 temporals, the outermost being the 

 larger and forming the hinder 

 border of the auditory notch. The 

 inner or median pair of supra- 

 temporals are commonly described 

 as supraoccipitals (so), and the outer 

 or lateral pair as " epiotics " (ep), 

 although clearly of dermal origin. 

 The plate anterior to the epiotic is 

 usually called the squamosal (sq), 

 and in front of this lie the post- 

 orbitals (por) and large, posterior 

 cheek plate (st), which is also iden- 

 tified with the supratemporals. The 

 two last-named pairs, together with 

 the so-called epiotics, are wanting in 

 all modern amphibians. Anterior 

 to the parietals and between the 

 orbits is a pair of usually elongate narrow frontals, and anterior to these a 

 pair of large nasals with openings for the external nares at their antero-lateral 

 angles. A pair of curved dentigerous pi-eraaxillae (pinx) terminate the snout 

 in front. 



The frontals rarely enter into the border of the orbits. These openings 

 are usually bounded behind by the post- 

 orbital and postfrontal, the latter plate 

 being invariably present ; mesially by 

 the postfrontal and prefrontal ; and 

 exteriorly by a long cheek plate called 

 the jugal. Very often a narrow tri- 

 angular bone, the lachrymal, is inserted 

 between the prefrontal and jugal, but 

 is usually pushed forward in advance 

 of the orbit. The postero- inferior 

 cranial angle is formed by the quadrato- 

 jugal, which sometimes develops a pro- 

 cess on the under side for articulation 

 with the lower jaw. In some of the 

 larger Stegocephalians the distal end 

 of this process is separated off from the 

 quadrato-jugal by a suture, and forms 

 a distinct quadrate bone. Joining the 

 quadrato-jugal in front is the maxillary, 

 a long, narrow, gently curved bone, which completes the outer border of 

 the cranium as far as the premaxillae. 



Most Palaeozoic Stegocephalians had the basiocciput cartilaginous, but in 

 the Labyrinthodonts and certain other forms the supratemporals are followed 



OLnJ 



Fiii. L'Ol. 



Palatal aspect of the skull of Branchioscmrvs. Re- 

 stored. 2/1 (after Credner). Pmx, Premaxilla; Mx, 

 .Maxilla ; QiiJ, Quadrato-jugal ; Ft, Pterygoid ; PSph, 

 Presphenoid ; PI, Palatine ; Vo, Vomer. 



