64 THORACIC AND LUMBAR VERTEBRAE. [CHAP. 



vertebra, placed to the inner side of the metapophysis, which 

 is now situated on a process projecting forwards into the 

 notch between the two upper articular facets of the antece- 

 dent vertebra. So that there are now three distinct articu- 

 lations connecting the arches of the vertebraj on each side, 

 the processes of the vertebrae which bear them interlocking 

 in a " tenon and mortise " fashion. 



This condition continues as far as the second lumbar, in 

 which, in addition to these three facets, a fourth (ps 3 is) 

 developed on the under-surface of the hinder edge of the 

 transverse process near its outer extremity, which articulates 

 with a similar facet (az 3) on the upper-surface of the 

 transverse process of the third lumbar, so that there are now 

 four pairs of articular facets, or zygapophyses, on each arch. 

 The same occurs also between the third lumbar and the 

 first sacral vertebra. 



In the Armadillos the lumbar metapophyses are very long, 

 and project upwards, outwards, and forwards, supporting 

 the bony carapace, while the broad transverse processes are 

 exceedingly reduced. 



An allied extinct genus, Glyptodon, had the greater number 

 of the trunk vertebrae completely ankylosed, a condition 

 altogether unique in the Mammalia. 



In neither of the Old World Edentates, Mam's and 

 Orycteropus, is there any development of the articular facets, 

 other than the ordinary zygapophyses. In the former genus 

 the metapophyses (contrary to the usual rule) project rather 

 backwards than forwards. The anterior zygapophyses of the 

 lumbar and posterior thoracic regions are largely developed) 

 and very concave, completely embracing the semicylindrical 

 surfaces of the posterior zygapophyses. There are no 

 distinct anapophyses. In Orycteropus the lumbar vertebra? 

 are numerous (8), with carinated bodies, long and slender 



