118 SAUROPTEEYGIA. 



SYNAPTOSAUEIAN BEANCH. 



In the two orders — Sauropterygia and Chelonia — of this branch 

 the following common features may be noted : — 



Quadrate firmly attached to cranium ; palate more or less com- 

 pletely closed, the pterygoids usually extending forwards to unite 

 with the vomers, when the latter are present ; one or two temporal 

 arcades ; and a parietal foramen at least in the young. No sclerotic 

 plates. Dorsal ribs as a rule with single heads 1 , and articulating 

 either at the junction of two centra, or with a facet or transverse 

 process placed entirely on the arch ; cervical ribs, when present, 

 articulating with double or single facets placed on the centrum. 

 No uncinate processes to ribs. Sacral ribs connected with the 

 vertebras by upper and lower articulations. Either abdominal ribs 

 or a plastron on ventral aspect of body. Chevrons, when present, 

 attached mainly or entirely to the posterior border of the centra : 

 not more than two sacrals. 



In the pectoral girdle the precoracoid 2 , when present, anchylosing 

 to the scapula ; and in the pelvis the pubis and ischium with flat 

 and expanded ventral surfaces, while the obturator foramen may 

 be completed by the union of the ischium with the pubis of the same 

 side. Limb-bones and vertebral centra with roughened epiphysial 

 terminal surfaces. The humerus may have either an entepicondylar 

 (ulnar) foramen, or an ectepicondylar groove, or both of these 

 together, or neither ; and the tarsus may be of a very primitive type. 

 Both pairs of limbs are present, and are generally subequal in length. 



Order SAUROPTERYGIA. 



Body devoid of exoskeleton ; with the neck more or less elon- 

 gated, and the tail short. Superior temporal arcade present 3 ; 

 narial apertures double and more or less approximated to orbit ; 



1 Baur ( Journ. Morphol. vol. i. p. 97) regards these heads as morphologically 

 double, owing to the union of capitulum and tuberculum. 



2 Huxley, ' Anatomy of Vertebrated Animals,' 1st ed. pp. 206, 222, re- 

 gards the precoracoidal process of the Lacertian coracoid as homologous with 

 the Chelonian and Amphibian precoracoid. 



3 Huxley, ' Anatomy of Vertebrated Animals,' lsted. p. 212, considered that 

 there were two arcades ; but Baur, ' Journ. Morphol.' vol. i. p. 97, rightly states 

 that the lower one is wanting 



