short and small, of little service for muscular attachment, unlike the scapulae of tail-propelling aquatic reptiles.
Probably the great development of the ventral elements of the pectoral and pelvic girdles in the plesiosaurs implies greatest development of the ventral muscles, used in the antero-posterior and downward movement of the paddles. A clavicular process of the coracoids of the later plesiosaurs (Fig. 102) extends forward to articulate with the proscapular process or with the clavicles. The mode of development of the proscapular process, as shown by Andrews, proves that it is an exogenous process of the scapula, corresponding to the acromion and not to the procoracoid, as it was once thought to do. The scapulae of tail-propelling aquatic reptiles are always short and broad, fan-shaped (Figs. 85, 112). The scapula of the Chelonia is also peculiar (Fig. 109 b, c, d). Enclosed within the thoracic cavity it has two rather slender branches, one extending toward the roof; the other, the proscapular process, springing from near the articular fossa, is directed downward and inward to be attached by ligaments to the interclavicle or entoplastron. Formerly this process was also supposed to be a separate ossification, the procoracoid, fused with the scapula, and on the strength of it a relationship was found with the plesiosaurs. It is now known to be an exogenous process of the scapula. The coracoid is more or less flattened and dilated at its extremity. It is directed inward and backward, and is connected with its mate by ligaments. In Stegochelys, a Triassic turtle, the proscapular process is small (Fig. 100).
In Eunotosaurus, a Permian genus of South Africa, that has been referred to the Chelonia in a wide sense, the pectoral girdle is of the primitive type, having a moderately long scapula, slender clavicles, and interclavicle, and the two coracoids approximating their mates in the median line.
A distinctly differentiated acromion process occurs in reptiles only among the Pariasauridae and especially the therapsids, mammal-like forms from South Africa. A distinct angular process on the front margin of the scapula in the Cotylosauria (Fig. 96 b, c) and Theromorpha (Figs. 96 d, 106), to which the clavicle is attached, however, corresponds to the acromion.
In general, the shorter and stouter are the legs, the shorter and broader are the scapulae. In upright-walking reptiles the scapula is
