PROFESSOR OWEN ON THE MEGATHERIUM. 763 
Fig. 49. A back view of the first dorsal vertebra, showing the diverging hypapophysial 
plates {hj, hy). 
Fig. 50. A back view of the second dorsal vertebra, showing the common base of the 
diverging plates {hy, hy). 
Fig. 31. A front view of the fourth dorsal vertebra, showing the elongated base of 
the bifurcating hypapophysis {hy). In this vertebra the anterior surface of 
the centrum is simply convex, the posterior surface concave. 
Fig. 52. A back view of the third cervical vertebra of a Crocodile, showing the 
diapophysis {d) and the parapophysis {p), or the upper and lower transverse 
processes of the right side ; and the same, on the left side, with the co- 
articuiated ‘ pleurapophysis ’ {pi) or ‘ hatchet-bone.’ c is the ball on the 
back part of the centrum ; n the neural arch ; ns the neural spine ; 2 is 
the prozygapophysis : z' the zygapophysis ; hy the hypapophysis. 
Fig. 53. Front view of part of the atlas of a Soft-tortoise {Trionyx Dumerili, O.). 
c the vacant space left by the absent centrum ; hy the hypapophysis or 
‘wedge-bone’; n the neural canal ; n' the anterior articular surface of the 
neurapophysis ; d the diapophysis. 
Fig. 54. Side view of the atlas of the same Trionyx, c the centrum ; hy hypapophysis; 
n neurapophysis, its anterior articular process or prozygapophysis ; z' zyg- 
apophysis. 
Fig. 55. Anterior view of the centrum of the atlas, showing c its articular surface for 
the hypapophysis; cn its articular surface for its neurapophyses, and for 
the basioccipital or centrum of the occipital vertebra. 
Fig. 56. Side view of the same ; x the concave articular surface for the centrum of 
the dentata. 
Fig. 57 . Front view of the atlas of the Long-necked Tortoise {Hydraspis longicollis, 
Bell). 
Fig. 58. Side view of the same vertebra. The centrum c (‘odontoid process’ of An- 
thropotomy) has coalesced with its neural arch w, and the typical character 
of the atlas, as it is manifested in the class of fishes and in enaliosaurians, 
is resumed ; hy, the hypapophysis (‘ body of the atlas’ in Anthropotomy). 
Fig. 59. The eighth cervical vertebra of the Hydraspis longicollis, which, like the 
first caudal vertebra of the Crocodiles*, is biconvex; c the centrum; % the 
two prozygapophyses ; z' the postzygapophysis ; d the two diapophyses. 
PLATE LIII. 
Fig. 60. A front view of the first caudal vertebra of the Great Ant-eater {Myrmeco- 
phaga juhata) . 
c. The centrum. 
n,n. The neurapophyses. 
* Physiological Catalogue of the Museum of the Royal College of Surgeons, vol. i. (1S33) p. 53, Prep, 
No. 250. 
