THE RIBS AND STERNUM 



115 



interlocking ends. Such ribs gave great strength to the lumbar 

 region, and are perhaps analogous to the greatly expanded trans- 

 verse processes of the crocodiles. 



The first four to six ribs of the Cotylosauria, and rarely also of the 

 Theromorpha, are progressively flattened and dilated, sometin^es, as 



Fig. 89. Plesiosaur vertebrae: Polycotylus. Cervical vertebrae from the side and behind, and 

 dorsal vertebrae from in front: «2, anterior zygapophysis; />3, posterior zygapop hysis; r,r,r, 

 cervical ribs; d, articulation of dorsal rib. 



Fig. 90. Vertebrae of gavial from the side (cervical), and from in front (dorsal): az, an- 

 terior zygapophysis; pz, posterior zygapophysis; d, diapophysis; r, cervical rib; c, articu- 

 lation for head; /, for tubercle of dorsal rib. 



in Diadectes and Limnoscelis (Fig. 95), remarkably so, for the direct 

 support of the short and broad scapula. Not only are these ribs so 

 remarkably dilated in Diadectes, but, continuing the expansion back- 

 ward, there are three flat dermal plates overlying the following ribs. 

 The cervical ribs of the Crocodilia (Fig. 90) and Dinosauria are 



