56 TRUNK VERTEBRAE. [chap. 



of each lumbar vertebra, having on its inner surface a facet, 

 which articulates with a corresponding facet on the anterior 

 edge of the arch of the succeeding vertebra, below the 

 ordinary zygapophysis. 



In Megatherium^ Myrniecophaga, CydotJmrus, and Dasypus 

 (in fact, all the remaining American Edentates), a disposition 

 thus slightly indicated in the Sloths, is carried out to a great 

 extent, and results in a very complex and altogether peculiar 

 method of articulation between the vertebrce. 



It will be most convenient to describe it from one species, 

 the Qtx^dX h^W.&dX^x {Myn?iecophaga jubata), but it is the same 

 in principle in all the above-named genera. 



Fig. 22. — Side view of twelfth and thirteenth thoracic vertebrae of Great Anteater 

 {Myrmecnpkaga jnbata), §. ;// metapophysis ; ic facet for articulation of tubercle 

 of rib; cc ditto for capitulum of rib: az anterior zygapophysis; as^ additi mal 

 anterior articular facet ; /;:: posterior zygapophysis ; J>z^ and J>z'^ additional pos- 

 terior articular facets. 



The anterior thoracic vertebrae articulate in a perfectly 

 normal manner by large anterior and posterior zygapophyses. 

 These retain the horizontal position of their facets through- 

 out. On the eleventh dorsal vertebra, the upper surface of 

 the backward projecting process which bears the posterior 

 zygapophysis {pz) below, develops an articular surface 



