PROFESSOR OWEN ON THE MEGATHERIUM. 
375 
vical and first dorsal vertebrae: the short neck quickly expands into the shaft of the 
rib : a small elliptical surface, fig. 1 a, w", on the upper part of the neck, is continued 
at its outer end into the larger convex surface upon the upper part of the tubercle, 
d!'\ from the middle of the anterior border of this surface a strong ridge is continued 
down the outer surface of the rib to its hinder border. The sternal end of the heem- 
apophysis, fig. 1 b, presents a large subtriangular surface, slightly concave in one 
direction, slightly convex in the other, adapted to a similar single concavo-convex 
surface on the side of the much developed and modified haemal spine called ‘ manu- 
brium sterni.’ 
This bone (Plate XXVII. figs. 1, 2, 3) is of an oval or cordiform figure, with a pro- 
minence on each side near its inferior truncated apex, below the lateral articulations, 
kp, for the first pair of sternal ribs. The outer surface is principally concave length- 
wise, and is sculptured by the impressions of the coarse aponeurotic structures which 
have been adherent to it in the living animal: a short median longitudinal ridge pro- 
jects from its lower part. The inner surface is chiefly convex, but is very irregular. 
At its upper half a strong median proniinence divides the shallow rough depressions, 
cl, for the attachment of the clavicular ligaments : these depressions are deepest above 
the costal articulations which are supported on well-marked triangular prominences. 
Between these prominences the bone is rather concave. A strong rough tuberosity 
projects below the lower angle of the costal surface. The contracted inferior end of 
the manubrium terminates in an oval convex articular surface, s', for the second ster- 
nal bone. There are no articular surfaces for the heemapophyses of the second dorsal 
segment. 
The skeletal segment (Plates XVII. Ct, XX. fig. 7) in advance of the first of 
the dorsal series is reduced to its centrum and neural arch ; both pleurapophysis, 
hsernapophysis and haemal spine are absent ; and its remaining anchylosed elements 
constitute the ‘seventh cervical vertebra’ of Descriptive Anatomy. This is most 
remarkable for the great development of the neural spine (Plate XX. fig. 7, ns), 
which exceeds that of the first dorsal vertebra: the summit is similarly expanded 
and flattened above (Plate XX. fig. 5, ns 7) ; but the anterior maigin is still more 
produced, forming a low angle about half-way down the spine (fig. 7? ns). The 
anterior zygapophyses are more remote from each other than in the first dorsal, and 
their articular surfaces are chiefly supported by the inner side of the base of the 
metapophyses, figs. 5, 7 ni, which are here well developed and more distinct from the 
diapophyses, d, fig. 7, than in the dorsal region. The diapophyses, figs. 5 ScJ, d, are 
strong, rugged, stand out from the sides of the neural arch, and terminate in rough 
truncate ends- The posterior zygapophyses (figs. 6 & 7, z') are slightly convex. 
In the sixth cervical vertebra (Plates XVII. Ce; XXL figs. 5 & 6) the spine, ns, is 
much shortened, though still long and large in proportion to the neural arch. The 
metapophyses, m, m, stand out from the upper part of the side of the neural arch 
behind the anterior zygapophyses, The diapophyses, d, d, are developed from the 
MDCCCLV. 3 E 
