68 



COMPARATIVE ANATOMY 



the ribs of Hatteria are broadened out and articulate both with 

 the centra and arches, thus indicating a differentiation into a 

 capitulum and a tuberculum (cf. p 69.). 



In Chelonians the cervical ribs unite with the vertebrae more 

 or less completely, and in the region of the trunk the ribs become 

 broadened out to form the costal plates of the carapace (p. 43). 



St, 



FIG. 53. SKELETON OF THE TRUNK OF A FALCON. 



Ca, coracoicl, which articulates with the sternum (St) at f ; Cr, keel of sternum ; 

 Fu(Cl), furcula (clavicles) ; O, glenoid cavity for humerus ; 8, scapula ; 

 V, vertebral, and Sp, sternal, portion of rib ; Un, uncinate process. 



Their proximal unbifurcated ends are attached between the centra, 

 at the junction of centrum and arch. There is no sternum. 



The proximal ends of the cervical ribs in the Crocodilia are 

 bifurcated, in correspondence with the double transverse processes 

 in this region, and thus a vertebrarterial canal is formed (cf. p. 59). 

 Further back, the ribs increase in length, and become segmented 

 into two or three articulated portions. In passing from before 

 backwards, their point of origin becomes gradually shifted, so that 

 while the anterior thoracic ribs are attached to the centra, the 



