54 The Alligator and Its Allies 



thin and triangular in shape, resembling in contour 

 a large, mammalian epiglottis. It forms an arch 

 over the space between the skull and the front 

 of the atlas proper. Reynolds calls it the pro- 

 atlas. 



The Axis. The centrum differs from those fol- 

 lowing it (described above) mainly in its close 

 articulation (not fusion) with the large odontoid 

 process; this process not only projects into the 

 atlas, as is usually the case, but articulates with its 

 postero-lateral border on each side, and is dis- 

 tinctly visible in a lateral view of the neck (Fig. 17, 

 3) . Like the rest of the cervical vertebras the poste- 

 rior surface of the centrum is convex. The neural 

 arch of the atlas differs from those following 

 mainly in having a much wider (in an antero-pos- 

 terior direction) neural spine. The lateral pro- 

 cesses and those bearing the prezygapophyses are 

 also less strongly developed than on the following 

 vertebras. 



The Thoracic Vertebra. The first thoracic verte- 

 bra differs scarcely at all from the ninth cervical; 

 and the tenth thoracic differs from the first lumbar 

 only in bearing a short rib. Only the first three 

 thoracic centra bear the hypapophyses noted in 

 connection with the cervical vertebras. The ribs 

 of the first two thoracic vertebras articulate with 

 them by two processes, as in the typical cervical 

 vertebras; the other ribs articulate only with the 

 transverse process. The fourth thoracic may be 



