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, Myrmecophaga, Cydothurus, 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 vertebrae. 



It will be most convenienrto describe it from one species, 

 the Great AxiteaXer (Myrmecophaga 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 

 (Myrinecnphaga jubata), g. ;// metapophysis ; tc facet for articulation of tubercle 

 of rib; cc ditto for capitulum of rib; az anterior zygapophysis; az 1 additional 

 anterior articular facet; pz posterior zygapophysis; pz 1 and pz 2 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 



