1859.] OWEN REPTILIAN FOSSILS. 57 



To the outer end of each of these bones seems to have been con- 

 nected or articulated a long slender bone (ib. 46), with a slight 

 sigmoid curve, directed backward. The following appear to be the 

 homologies of the foregoing bones. The median and most posterior 

 of them is the uro-hyal, no. 43. The transverse pair answer to the 

 hindmost pair, a a, in the hyoid of the Tortoise, figured by Cuvier* 

 in the ' Ossemens Fossiles,' 4to, torn. v. pt. ii. pi. 12. fig. 42 (my 

 " basibranchial," no. 45). The longitudinal pah- appended to them 

 answer to c in the same figure (my " hypobranchials," no. 46 f ). 



In advance of the left basibranchial is a flattened broad lanielli- 

 form bone with the fore and hind borders convex, the outer and 

 inner ones concave ; but the median or inner border of this plate 

 is not entire. The bone in question may be either a median sym- 

 metrical piece, like the uro-hyal, but displaced ; or it may be the left 

 of a pair of plates, answering in that case to the middle pair, a a, 

 in the above-cited figure of the hyoid of the tortoise. I incline to 

 the latter opinion, and believe it to be the half of abasi-hyal, no. 41, 

 divided in the median line. 



To the outer concavity of this bone has been attached the end of 

 a long and strong bone, flattened and gradually expanded at both 

 ends ; it is directed outward and backward. It is a large and strong 

 cerato-hyal, no. 40, and is double the length of the hypobranchial or 

 posterior " cornu." 



The lower jaw in the skull, showing the above-described hyoid 

 apparatus, is 4-A- inches long. The length of the cerato-hyal is Sc- 

 inches : that of the hypobranchial is 2i inches. The length of the 

 uro-hyal, 4, is 1 inch ; its breadth is nearly the same. 



At the fore part of this lower jaw the intercalation of the fore end 

 of the angular element (31) between the splenial (32) and dentary (33) 

 is well shown. 



In the Crocodilians there is a broad cartilaginous basi-hyal 

 suspended by a pair of strong bony cerato-hyals ; but there are no 

 distinct thyro-hyals (hypobranchials), nor any uro-hyals. 



In Lacertians there are both cerato- and thyro-hyals ; and in 

 some genera of Iguanians and Lizards proper (Lacerta, Cuv.) there 

 is a long and slender bifurcated uro-byal or pair of uro-hyals. The 

 thyro-hyals are not supported on distinct bones, answering to the 

 basihranchials, 48. 



In Chelonians the oro-hyal is wanting ; but in some species | '/',>•- 

 tudo > lephantopvs) the th\ ro-hyals or hypobranchials are articulated 

 to a pair of boms answering to the basibranchials in Fishes, which 

 diverge from each other to form those articulations. 



In Oudenodon, and probably also in l)i,i/ )t ()(/oii, the type of the 

 hyoid apparatus conforms most with thai in the Chdon&a, but com- 

 bines therewith certain Lacertian characters. 



In the composition and general form of the skull Oudmodon 



so closely resembles Dicynodon and Ptychoanathus as to indicate a 



general family relationship. Viewing, indeed, the ridged indication 

 * Archetype of the Vertebrate Skeleton - tl p 71 



