742 
PROFESSOR OWEN ON THE MEGATHERIUM. 
vertebrse. The anapophysis {a) commences on the seventh dorsal, projecting back- 
wards behind the base of the diapophysis, and presenting on its upper side an arti- 
cular surface for that beneath the base of the succeeding metapophysis. The anapo- 
physis increases in length, but more so in vertical thickness in the succeeding ver- 
tebrse. The diapophysis {d) subsides to a mere ridge in the last dorsal and disap- 
pears in the lumbar vertebrse, where the transverse processes are formed by parapo- 
physes. In the penultimate dorsal vertebra the anapophysis is notched posteriorly, 
and developes a small surface from below its inferior division for articulating with 
the head of the last rib. The succeeding anapophysis developes a similar surface for 
articulating with a short and thick exogenous process or ‘ parapophysis’: and this 
complex condition of the anapophysis is continued throughout the lumbar region, the 
last vertebra having a longer and narrower anapophysis. Thus on each side of the 
fore-part of each lumbar vertebra there is one articular surface on the prozygapophysis, 
a second on the inner side of the base of the metapophysis, a third on the outer and 
under side of the same base, and a fourth on the upper side of the base of the para- 
pophysis ; and on each side of the back part of the same vertebrae there is one articular 
surface on the under side, and ct second on the outer side of the posterior zygapophysis, 
a third surface on the upper, and a fourth on the under side of the anapophysis ; 
making sixteen synovial joints, four on each side of both fore and back parts of the 
vertebrae, which joints may be called, beginning from above downwards, the ‘ zyg- 
apophysial,’ ‘metapophysial,’ ‘anapophysial’ and ‘parapophysial’ articulations respect- 
ively* ; and the power of inflecting the substantive names for the several processes 
and applying them adjectively to such modifications as I have described is not one of 
the least advantages of such substantive names to the descriptive Anatomist. These 
different articulations form double tenon-and-mortise joints on each side of the ver- 
tebrse. But their comparison with these joints in artificial carpentry, affords but a 
meagre idea of their true nature and complexity, whilst the supposition of their 
homology with the similar tenon-and-mortise joints of the backbone of Serpents is, 
as I shall presently demonstrate, unsupported by exact comparison. 
In the Dasypus tricinctus, the true or moveable vertebrse present the following, 
amongst other, characters : — 
The spine of the third cervical has completely coalesced with that of the dentata, 
which is thick and high, but more extended forwards than backwards. The spine of 
the fourth cervical is applied to its back part. The neural arches of the succeeding 
cervicals have no spines, but form thin transverse bars of bone above, which are 
incomplete in the middle at the fifth and sixth cervicals, upon which the rest are 
strongly bent backwards. Their bodies are extremely broad in proportion to their 
length or antero-posterior diameter. The articular bed for the head and tubercle of 
the first dorsal rib is contributed to in equal shares by the last cervical and first 
* The zygapophysial and metapojihysial synovial sacs communicate and form a common joint in the posterior 
dorsal and lumbar vertebrcC. 
