EDENTATA OF THE SANTA CRUZ BEDS. 25 



The third and fourth thoracics have smaller, but still broad, depressed 

 and opisthocoelous centra, and very small and low neural canal ; the 

 neural spines are slender and have a more decided backward inclination 

 than those of the first and second vertebrae ; the transverse processes are 

 long, subcylindrical and upturned at the end, where they bear facets for 

 the tubercles of the ribs and indicate that in this region the ribs had long 

 necks. As in Tatu, each transverse process is pierced by a foramen which 

 enters the process on the posterior and opens on the ventral side. Minute, 

 incipient metapophyses are present on the fourth vertebra, arising from the 

 front side of the transverse processes, near the base. 



The last five thoracic vertebras gradually take on the characters of the 

 lumbars. The centra, which are remarkably depressed throughout, grow 

 larger posteriorly ; the neural spines become shorter, heavier, less strongly 

 inclined backward, more expanded and thickened at the free end ; the meta- 

 pophyses increase rapidly in size, until, on the last vertebra, they are as 

 long as the spine, inclining steeply forward and outward ; the transverse 

 processes diminish as the metapophyses increase and are very short on all 

 of these vertebrae. On the tenth and eleventh vertebrae (assuming that 

 eleven is the number of the thoracics) the facet for the tubercle of the rib 

 is brought into immediate juxtaposition to that for the head, which, on the 

 tenth and especially on the eleventh, is very large, prominently projecting 

 and deeply concave ; the perforation of the transverse processes continues 

 as far back as the eighth vertebra. The accessory articular processes are 

 already present on the seventh vertebra and they may well have been 

 present on the sixth, as they are in Tatu. On the seventh thoracic the 

 postzygapophyses, though still very small, are of the lumbar type and an 

 articular surface is developed on the anapophysis, which is overlapped by 

 a corresponding facet on the metapophysis of the eighth vertebra, and thus 

 there are two pairs of postzygapophyses on the seventh and of prezygapoph- 

 yses on the eighth. Between the ninth and tenth vetebrae an additional 

 pair of articulations is developed, a posterior one on the ventral side of the 

 anapophysis of the eighth and an anterior one on the dorsal side of the 

 transverse process of the ninth. On the last two thoracics these articular 

 surfaces become larger and more conspicuous. 



The last four thoracic vertebrae have deep grooves on the sides of the 

 centra, extending downward and forward from the intervertebral foramina 

 and continued anteriorly upon the ventral side ; they become deeper on 



