78 The Alligator 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 partially 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 
vertebre. 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 typical 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- 
