42 Messrs. Embleton and Atthey on the 



are bounded by the nasals and prefrontals at their inner, and 

 by the maxillaries and malars at their outer border. 



The frontals are narrow and elongated, slightly broader 

 behind than before, united in front to the nasals, behind to the 

 parietals,and on their outsides to the prefrontals for three fourths 

 of their length, and to the postfrontals for the remaining one 

 fourth. The median suture unites them to each other. 



The prefrontals, elongated and about half as wide as the 

 frontals, become gradually wider from back to front ; they 

 rest upon the postfrontals behind, upon three fourths of the 

 frontals at their inner sides, and form three fourths of the inner 

 edges of the orbital openings at their outer side. Just in front 

 of the suture uniting the pre- and postfrontals, at the outer 

 margins of the bones is a small but distinct prominence, mark- 

 ing the boundary, on that side, of the true orbit. In front, the 

 sharply wedge-shaped ends of the prefrontals are received into 

 retreating angles formed by the diverging sides of the nasals 

 and lacrymals. 



The postfrontals are rather more than half the length of the 

 prefrontals, somewhat hatchet-shaped, the handle forwards, 

 and joining the prefrontals ; their inner edges are bounded 

 almost equally by the frontals and parietals ; posteriorly they 

 abut upon the squamous bones, and externally, besides joining 

 with the postorbitals, form smooth rounded concave edges, 

 which look outwards and forwards, and constitute a consider- 

 able part of the inner border of the true orbit. 



The parietals are a good deal shorter, but on the whole 

 broader, than the frontals, with the posterior borders of which 

 they articulate. They are much broader behind than in front, 

 and are joined outside by the postfrontals and squamous bones, 

 and behind with the pair of bones to be next mentioned. 



The parietal foramen has been already noticed. 



The pair of bones next behind and articulating with the 

 parietals, and which, united on the median line, overhang the 

 occipital segment of the skull, as the parietals themselves in 

 most Vertebrata do, correspond to the pair called " supra- 

 occipitals " by Von Meyer in his description of Archegosaurus, 

 in his work entitled ' Reptilien aus der Steinkohlen-Forma- 

 tion in Deutschland.' They are irregular squares of about 

 | inch on a side ; their outer borders are bounded for a short 

 space anteriorly by the squamous, and further back by the 

 mastoids ; behind they articulate on each side of the median 

 line with the upper border of what appears to be the true 

 supraoccipital, and, further out, slightly with the exoccipitals. 

 They form with the mastoids the posterior border of the top 

 of the cranium. 



