398 ANATOMY OF VERTEBRATES. 



between the diapophysis and anterior zygapopliysis, and repeats 

 the same articnlation with the anapophysis. In the last two 

 dorsal vertebra?, the base of the metapophysis developes a second 

 articular surface from its inner side, which joins a new or acces- 

 sory articular surface on the outside of the posterior zygapophysis 

 of the antecedent vertebra. This tenon-and-mortice articulation 

 of the metapophysis with the zygapophysis on the inner side and 

 with the anapophysis on the outer side, is repeated throughout 

 the whole lumbar series. The anapophysis begins to be developed 

 from the anterior dorsal vertebra, and even there presents an 

 articular surface at its under part to join a corresponding surface 

 on a parapophysis developed from the fore and outer part of 

 the neural arch of the succeeding vertebra. In the tenth dorsal 

 a second articular surface is established in the upper part of the 

 anapophyses for the inferior metapophysial one of the succeeding 

 vertebra ; here, therefore, the anapophysis begins to be morticed 

 between the parapophysial and metapophysial articular surfaces, 

 which surfaces continue to the antepenultimate lumbar vertebra, 

 from which, forward, to the eleventh dorsal, there are sixteen 

 joints between each pair of vertebrae. But this complication goes 

 further ; for, in the penultimate lumbar vertebra, a third articular 

 surface is developed from the under and outer part of the anapo- 

 physis, which joins an articular surface on the upper and fore part 

 of the diapophysis of the last lumbar : and this vertebra is united 

 in a similarly complex manner with the first sacral vertebra, 

 which would make eighteen synovial joints, in addition to those 

 at the ends of the centrum, but that those between the normal 

 articular processes, or zygapophyses, are now suppressed. The 

 true serial homology of the processes as ' parapophyses,' de- 

 veloped from the fore part of the base of the neural arch to 

 articulate Avith the under part of the anapophyses, is well illus- 

 trated by the vertebrae of the Great Anteater, as in the Mega- 

 therium, in which the true diapoj)hyses are better developed than 

 in the Armadillos. 



The spines of the sacrals, ib. s, blend into a bony ridge ; the 

 transverse processes of the last three join the ischia. Ha3mal 

 arches articulate with the intervals of most of the caudal 

 vertebrae. 



In the little Two-toed Anteater the dorsal pleurapophyses show 

 a chelonian expansion ; but overlap, or join by squamous instead 

 of dentate sutures. 



In the Ai {Brachjpus tridactylus, fig. 263), the vertebral formula 

 is :— c 9, D 16, L 3, s 6, cd 11. The neural arch of the atlas is 



