PROFESSOR OWEN ON THE MEGATHERIUM. 
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The metapophysis, m, projects forward above the zygapophysis, the articular surface 
of which {z, fig. 5) is continued upward upon the metapophysis (mz, fig. 4), The 
anapophysis, a a, fig. 5, Plate XXVL, forms a strong thick square plate of bone pro- 
jecting upward, outward and backward from the diapophysis. The anapophysial 
articular surface, a', a\ fig. 5, Plate XIX., is on the under and back part of this plate, 
nearly parallel with the posterior zygapophysis, z', the convex inner border of which 
has increased in thickness. The body of the vertebra assumes, with its larger size, 
a more decided trihedral or wedge-shaped figure at this part of the spine. 
The rib of the thirteenth segment loses the convex articular surface on the tubercle, 
which is attached by ligaments to the diapophysis. The rib of the fourteenth seg- 
ment loses the small flat surface at the extremity of the head ; and only the large 
convex surface on the upper part of that end of the neck remains, which surface, 
extending to the free end of the neck, reduces that part to an edge : the tubercle 
exists in this rib, and is rough for ligamentous insertions as in the preceding. In the 
fifteenth (Plate XIX. figs, 1 and 3) and sixteenth {ib. fig. 2) ribs the tubercle subsides ; 
the neck of the rib is defined by the rugosity of its whole upper surface, save that 
part where the articular convexity, n", remains for articulating with the neural arch, 
as shown at n', fig. 5, Plate XIX. 
The haemal spine (‘ sterneber ’) of the eighth segment, Plate XXVII. figs. 8-12, may 
be the last of the so-called bones of the sternum. It is divided, like those in advance, 
into a peripheral and a central portion. The peripheral portion (fig. 9) is of a sub- 
quadrate form, the four corresponding articular surfaces {ha, ha!) for the haemapo- 
physes almost touching each other at their margins ; the outer roughened surface is 
convex; the anterior haemapophysial articular surface is suppressed on the left side of 
this division of the bone, fig. 10, to which the corresponding haemapophysis seems to 
have been united by ligament. The central division of the bone (fig. 8) presents the 
median flat surface {s, fig. 10) on its upper or fore-part for the antecedent sterneber, 
and the concave haemapophysial surface, hp,hp, on each side of its anterior half; but 
posteriorly the haemapophysial surface on each side is confluent with that of the 
same side belonging to the peripheral division of the bone, which thus presents at its 
lower or hinder part only two long oval concave articular surfaces {hp a, figs. 1 1 & 12) 
for the pair of haemapophyses of the ninth segment of the chest, and the concavities 
almost meet at the under surface of the sterneber, which there presents no articular 
surface for a succeeding one. The number of articular surfaces, therefore, of this 
bone is reduced to six; one, s, for the antecedent sterneber, two on the anterior half 
of the right side, hp, ha, fig. 12, for the bifid condyle of the eighth haemapophysis, 
one on the anterior half of the left side, ha, fig. 10, for one of the condyles of the 
opposite haemapophysis ; and a pair of surfaces on the posterior and lateral parts, hp a, 
for the ninth pair of haemapophyses which terminate each by a single convex condyle. 
It is possible that a more simplified sterneber may have intervened between the 
haemapophyses of the tenth segment. 
