The pectoral girdle is well developed in all groups of reptiles except the Ophidia, occurring even in the limbless Amphisbaenidae. It is very solid in the Theromorpha. As a rule all three cartilage bones, scapula, coracoid, and precoracoid are represented, and frequently also the membrane bones,--clavicles, and interclavicle. The coracoids are generally flat expanded bones, which sometimes, as in Sauropterygia and Ichthyosauria, meet in a ventral symphysis; sometimes, as in Lacertilia, are united with the sides of the sternum. In Chelonia neither the coracoids nor precoracoids meet one another, but their free ends are connected by fibrocartilaginous bands. In Lacertilia the coracoids are pierced by fenestrae. The precoracoid is generally represented, but the Theromorpha are the only reptiles in which it is separately ossified; it forms a well-marked process on the coracoid in Lacertilia (fig. 54, 5). It is absent in Ichthyosauria, and Dinosauria, and probably in Sauropterygia. In some Lacertilia and Chelonia the sternal ends of the coracoids are unossified and form epicoracoids; in some Chelonia there are also epiprecoracoids; but neither these nor the epicoracoids overlap their fellows of the opposite side as they do in arciferous Anura (see p. 185). In some Lacertilia with degenerate limbs the pectoral girdle is also much reduced, in _Ophisaurus apus_ the ventral borders of the coracoids are widely separated. A scapula is always present, and is generally expanded distally, but in the Chelonia the distal end is cylindrical. In the Theromorpha it has an acromial process with which the precoracoid articulates, and it is very large in Dinosauria. In the Chelonia the scapula and precoracoid are ossified continuously. Among the Pterosauria, _Pteranodon_ has an unique pectoral girdle; the scapula and coracoid are ankylosed and the scapula articulates with the neural spines of several ankylosed vertebrae. Clavicles occur in some Theromorpha such as _Pariasaurus_, and also in the Ichthyosauria, Sauropterygia, Rhynchocephalia, and most Lacertilia. They are absent in the Pterosauria, the Chamaeleons among Lacertilia, the Ophidia and the Crocodilia. They are wanting too in the Chelonia, unless the first pair of ossifications in the plastron are to be regarded as clavicles. In the Sauropterygia bones regarded as the clavicles and interclavicle are generally well developed. The unpaired ossification in the plastron of Chelonia is an interclavicle, and a representative of the same bone occurs arising from the sternum in Pterosauria. A well developed =T=-shaped interclavicle is found in Ichthyosauria, Rhynchocephalia, Lacertilia, and some Theromorpha, such as _Pariasaurus_. THE LIMBS.