402 



ANATOMY OF VERTEBRATES. 



Pelvis of the Mylodon robustus, posterior view. xc'. 



and complete the wide obturator hole, o. The tuberosity, /e, is not 

 well marked. 



The vertebral column shows neither in Mylodon nor Mega- 

 therium any apophysial de- 

 velopements related, as in 

 the Armadillos, to the sup- 

 port of a bony carapace. 



The Megatherium has C 

 7, D 16, L 3, S 5, Cd 18 ; fig. 

 279. The neural spines elon- 

 gate in the last two cervical, 

 and increase in both length 

 and breadth in the anterior 

 dorsal vertebrae. The dorsal 

 hajmapophyses are bony as 

 in the Mylodon, Sloths, 

 Anteaters, and Armadillos. 

 Nine pairs of ribs directly 

 articulate with the sternum, 

 which consists of eight bones. Most of the dorsal vertebrae 

 are peculiar in having a third, medial, zygapophysis between 

 the ordinary anterior and posterior pairs : they likewise present 

 three surfaces to the pleurapophysis, one on the centrum for 

 the ' head of the rib,' one on the neurapophysis for the ' neck,' 

 and one on the diapophysis for the ^tubercle.' The htemapo- 

 physes present analogous complex joints with the sternebers, 

 ha\dng a pair of condyles, synovially articulated with two pairs of 

 cavities on contiguous sternebers, each such sterneber presenting 

 ten articulations, one for the antecedent, another for the succeed- 

 ing sterneber, and two pairs of haimapophysial ca\dties on each 

 side. The posterior dorsal and lumbar vertebrae present, besides 

 the articular surfaces for the centrums, and those of the zygapo- 

 physes, also a pair of metapophysial and a pair of anapophysial 

 articulations.^ In the confluence of the anterior dorsal pleur- and 

 haem-apophyses the Megathere ^ resembles the Sloth. The caudal 

 vertebrae supporting, as in Mylodon, a powerful column, serving 

 as a prop to the massive hind part of the trunk when the fore 

 part is raised, as in fig. 267, have long and strong di- and haem- 

 apophyses : the latter separate in the first caudal, but coalesced at 

 their distal ends in the succeeding caudals to near the end of tlie 

 tail.^ 



XCI-. PI. iii. fiffs. 4 and 5. 



lb. PI. 



lb. Pis. ii. and viii. 



