3/0 
PROFESSOR OWEN ON THE MEGATHERIUM. 
out, or transversely, from the base of the neural arch, and affords a joint or a surface 
of confluence for the rib; this I have proposed to call ‘diapophysis*' : the second 
process has a range of variety in its position from the upper part of the diapophysis 
to that of the anterior zygapophysis, but, as it is commonly somewhere between these 
two, I have called it ‘ metapophysis'f'' ; the third process projects most commonly more 
or less backwards, from the base of the diapophysis, and I have termed it ‘ anapo- 
physisj^'. As each of the above processes developes in some species an articular 
surface, and as each is usually more or less oblique in position, I have called those 
processes which more constantly support such surfaces ‘ zygapophyses^. The com- 
parative anatomy of these and other ‘exogenous’ processes has been the subject of a 
previous part of this memoir, because their extreme degree of variety in the Order 
Edentata, and extraordinary development in the Armadillos and true Anteaters, 
render them of unusual importance in the question of the affinities of the Mega- 
therium. 
The narrow compressed base of the neurapophysis of the fifth dorsal vertebra in 
that animal having risen above the centrum, developes on its outer surface a large 
vertically oval articular surface, w', concave in the direction of its long axis, almost 
flat transversely ; to which surface a corresponding convex articular surface, w", on 
the upper part of the neck of the rib near the head, is adapted. Above the surface, 
n! , the diapophysis, d, stands out, short, thick, subdepressed, expanded at its extremity, 
which is slightly produced backwards and supports on its outer surface an elliptical 
articular concavity, d', with the long axis directed from above downwards and back- 
wards, and articulated to a corresponding convexity, d" , upon the tubercle of the rib. 
A rugged tuberosity, m, on the upper and fore-part of the diapophysis represents in 
rudiment the metapophysis. A smaller tuberosity is interposed between the anterior 
zygapophysis, 2 , and the neurapophysial surface, w', for tlie rib. Thus the neural 
arch of the vertebra in question presents ten distinct articulations besides the two 
sutural ones now obliterated by its anchylosis to the centrum, which part has its two 
large terminal articulations distinct from those for the head of the rib, d , which 
I reckon among the neurapophysial ones. The rib, which term 1 confine to the 
pleurapophysis, or ‘ vertebral rib’ of comparative anatomists, ‘ pars ossea costse’ of 
anthropotomy, presents a small flat subcircular surface, c", for articulation with that 
on the base of the neurapophysis forming the upper angle of the body of the vertebra 
in advance of the segment to which the rib belongs. The neck of the rib rapidly 
expands as it quits the head, developes the convex oval surface, n!', on its upper part 
* Lectures on the Comparative Anatomy of the Vertebrate Animals, 8vo, Longmans, 1846, vol. i. p. 42; 
from cid Irans, and uTr6(bv/Tis processus. 
f On the Anatomy of the Male Aurochs, Proceedings of the Zoological Society, November 14, 1848, p. 131, 
from perd inter, and u-rruivais. 
I On the Anatomy of the Aurochs, ut supra, p. 131 ; from dvd retro, and dirtxpvais. 
§ Lectures on the Comparative Anatomy of the Vertebrate Animals, p. 43 ; from ^vyov junctura, and 
drr6(jtvms ; these are called the “ oblique or articular processes” in Human Anatomy. 
