58 TRUNK VERTEBRAE. [chap. 



cedent vertebra. So that there are now three distinct arti- 

 culations connecting the arches of the vertebrae on each 

 side, the processes of the vertebras which bear them inter- 

 locking 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 (/ 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 con- 

 dition altogether unique in the Mammalia. 



In neither of the Old World Edentates, Mams 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 region are largely developed, 

 and very concave, completely embracing the semicylindrical 

 surfaces of the posterior zygapophyses. There are no 

 distinct anapophyses. In Orycteropus the lumbar vertebrae 

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

 spines inclined forwards, long, broad, and flat transverse pro- 

 cesses pointing forwards and downwards, well developed 

 metapophyses and rudimentary anapophyses. 



