EDENTATA OF THE SANTA CRUZ BEDS. 223 



cervical has a broader centrum than the sixth, with long, imperforate 

 transverse processes, which are slightly expanded at the distal end, ter- 

 minating in a recurved hook ; the neural arch is very narrow and the 

 spine, through far shorter and more slender than that of the first thoracic, 

 is yet much larger than on any other cervical. 



As a whole, the neck is short and slender, narrowing posteriorly, but 

 increasing in dorso-ventral thickness, owing to the successively longer 

 spines. 



The first thoracic has a centrum which about equals in size that of the 

 seventh cervical, and the prezygapophyses are of cervical type ; the neural 

 canal is low and wide, the arch is very broad and the spine, though but 

 moderately developed, is yet the largest in the anterior part of the thorax ; 

 this spine is elongate, broad and quite thick, and is expanded at the tip, 

 making the anterior and posterior borders concave, but with only a slight 

 backward inclination. The transverse processes are long, straight and ex- 

 panded at the ends, which bear deep concavities for the tubercles of the 

 first pair of ribs. The second thoracic differs considerably from the first, 

 having a smaller centrum, much shorter transverse processes, and a 

 longer, more slender and more inclined neural spine ; the prezygapophyses 

 are still quite widely separated by a deep notch. In the succeeding 

 vertebrae the centra are reduced, their small size in this region being one 

 of the most characteristic features of the vertebral column ; the neural 

 spines become shorter, more slender and more steeply inclined ; the 

 transverse processes shorter and small, club-like metapophyses begin to 

 appear upon their bases. 



This type of vertebra continues to the eight thoracic, after which the 

 centra begin to enlarge and increase regularly in size backward, those in 

 the hinder part of the region being far larger than those in the forward 

 part ; on the last nine vertebrae are the two foramina opening on the ven- 

 tral side of the centra, though, for the most part, these foramina are 

 quite small. The neural arches are very broad in both directions and the 

 spines become broader, thicker and more erect, though the spines of all 

 the trunk-vertebrae have a more or less decided backward inclination. 

 The last four thoracic vertebrae are of quite a different type from those 

 which precede them and are unlike the lumbars ; the neural spines are 

 rather short, but broad antero-posteriorly, and have but a slight backward 

 slope ; the transverse processes bear no distinct facets for the tubercles of 



