THE SKELETON IN MAMMALIA. VERTEBRAL COLUMN. 447 



THORACO-LUMBAR, OR TRUNK VERTEBRAE. 



In the MONOTREMATA there are nineteen thoraco-lumbar 

 vertebrae, sixteen (Echidna) or seventeen (Ornithorhynchus) 

 of which bear ribs. The transverse processes are very short 

 and do not articulate with the ribs, which are united to the 

 centra only. 



In the MARSUPIALIA there are always nineteen thoraco- 

 lumbar vertebrae, thirteen of which generally bear ribs. The 

 lumbar vertebrae frequently have large metapophyses and 

 anapophyses, these being specially well seen in the Kangaroos 

 and Koala (Phascolarctus). 



The EDENTATA are very variable as regards their trunk 

 vertebrae. The two genera of Sloths differ much as regards 

 the number, for while Bradypus has only nineteen, fifteen or 

 sixteen of which bear ribs, Choloepus has twenty-seven, twenty- 

 four of which are thoracic, and bear ribs. In Bradypus a 

 small outgrowth from the transverse process articulates with 

 the neural arch of the succeeding vertebra. In both genera 

 the neural spines are all directed backwards. 



In the Megatheriidae as in the sloths the neural spines 

 are all directed backwards, and in the lumbar region additional 

 articulating surfaces occur, better developed than are those in 

 Bradypus. 



In the anteaters (Myrmecophagidae) there are seventeen 

 or eighteen thoraco-lumbar vertebrae, all of which except two 

 or three bear ribs. The posterior thoracic and anterior lumbar 

 vertebrae articulate in a very complex fashion, second, third, and 

 fourth pairs of zygapophyses being progressively developed in 

 addition to the ordinary ones, as the vertebrae are followed back. 



In the Armadillos the lumbar vertebrae have long meta- 

 pophyses which project upwards and forwards and help to 

 support the carapace. In Glyptodon almost all the thoraco- 

 lumbar vertebrae are completely ankylosed together. 



In the Manidae there are no additional zygapophyses but 

 the normal ones of the lumbar and posterior thoracic regions 



