i68 



VERTEBRATE SKELETON 



temporal fossa by a three-branched postfrontal, one ramus meeting the squa- 

 mosal to form the upper arcade. The orbits are bounded in front by prefrontal 

 and a process from the zygomatic. The large quadrate is fixed by squamosal 

 above and pterygoid below; no transversum occurs. The halves of the lower 

 jaw are fused at the symphysis. Each half consists of the typical six bones, 

 sutures persisting in some genera. Some species were toothless; others have the- 

 codont teeth in the margins of the jaws. Traces have been found of a slender 

 hj'oid. 



DINOSAURIA have a relatively small skull, which, in Saurischia, was carried 

 nearly in line with the vertebral column; in Ornithischia nearly at right angles 

 with it. The cranium of Theropoda is not completely ossified. Both temporal 

 fossae are present as is an antorbital vacuity of varying size, smallest or lacking 

 in Ornithischia. The sutures between the bones are frequently indistinct. 

 Sometimes the foramen m.agnum was bordered by the four occipitalia, some- 



FlG. i8i.— Skull of Ceralosaurus (Gilmore, '15). a, articulate; an, angulare; 

 d, dentale; m, maxilla; n, nasal; nh, nasal horn-core; p, parietal; pf, postfrontal; pm, 

 premaxilla; pt, pterygoid; q, quadrate; qj, quadratojugal; sa, surangulare; 55, squamosal; 

 c, zygomatic, g, goniale. 



times by exoccipitals alone, these bones sometimes being distinct, sometimes 

 more or less completely fused with the supraoccipital, and always with the 

 opisthotics, forming a parotic process on either side. No parietal foramen is 

 known. The frontals are paired, and in Ceratopsia each has a horn core (large 

 in some genera) and a third on the nasals. The orbits are large, and the nares, 

 usually far anterior, often lie between maxillas, premaxillae and nasals, but in 

 Ceratopsia, where they are very large, they are bounded in front by a rostral 

 bone, not known outside this group. The rather large premaxilla may bear 

 teeth or be edentulous, the teeth of both jaws being in alveolar grooves or 

 thecodont. 



The imperfectly known cranial floor, was somewhat like that of Rhyncho- 

 cephals, the palatines meeting in the middle line. Some have the pterygoids 

 approximate and some have an epipterygoid. The large quadrate is united by 



