78 The Alliu^ator and Its Allies 



with a well-marked vertebrarterial canal between 

 them. The ventral surface or capitulum articu- 

 lates with a short process on the centrum; the 

 dorsal surface or tuberculum (7) articulates with 

 the transverse process. The third to seventh ribs 

 are somewhat T-shaped, the stem of the T being 

 the tubercle and head, while the cross arm of the T 

 extends parallel to the axis of the neck (Fig. 17, 7). 

 In the eighth rib the posterior arm of the T is 

 elongated and projects out at a wide angle from the 

 body; and in the ninth or last cervical rib this 

 arm extends laterally as far as the vertebral portion 

 of the thoracic ribs and has a cartilaginous tip. 



The Thoracic Ribs (Figs. 16 and 26). These are 

 ten in number, the first eight pairs being connected 

 with the sternum. The fourth may be taken as 

 typical. It consists of a bony vertebral portion 

 and partiall}^ ossified intermediate and sternal 

 portions. The vertebral portion articulates with 

 its corresponding transverse process by two sur- 

 faces, as described in connection with the thoracic 

 vertebrae. In the first and second ribs only the 

 tuberculum articulates with the transverse process, 

 the head having a separate articular surface on the 

 side of the centrum, as in the t3'pical cervical rib. 

 In the last thoracic rib the head and tubercle 

 are not distinguishable from each other. Near the 

 distal end of all the vertebral portions except the 

 first and the last two ribs is a caudally projecting, 

 partially ossified, uncinate process. The inter- 



