PROFESSOR OWEN ON THE MEGATHERIUM. 
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dorsal vertebrae. Ten vertebrae show the impressions of the articulation of the head 
of the rib in addition to the first dorsal, and the neurapophyses of these eleven ver- 
tebrae are directly perforated by the spinal nerves, Plate XLIX., fig. 19, n, w*. The 
articulation for the last rib {pi) is as equally divided between the two contiguous 
vertebrae as is that of the first rib. The prominence {p) supporting the articular 
surface for the head of the rib answers to the parapophysis, just as the prominence 
for supporting the articulation for the tubercle of the rib, represents the diapophysis. 
The prominence in the first lumbar vertebra {p) which articulates with the under 
part of the anapophysis {a) of the last dorsal, repeats the prominence in that dorsal, 
which articulates with the head of the last rib ; it is therefore a parapophysis. The 
diapophysis {d) projects, as in the dorsal vertebrae, from the upper and outer part of 
the base of the short and thick anapophysis (a), and this anapophysis presents, as 
in other Armadillos, two articular surfaces, one above, for the under part of the 
metapophysis {m), another below, for the upper part of the parapophysis {p). Thus 
the vertebrae are interlocked by tenon-and-mortise joints, as Cuvier has described, 
but it is by distinct parts of the vertebra from those which form the corresponding 
joints in the backbone of serpents. 
The metapophysis (m, 7) begins in the seventh dorsal as a distinct process : the an- 
apophysis is first developed in the sixth {a 6), and articulates with the under part of the 
first metapophysis ; the subsequent metapophyses {ni, m) present the usual progressive 
and great development, as also the two joints, one on the inner and the other on the 
under side of their base. Nothing can be more distinct than the anterior and poste- 
rior zygapophyses of the sixth dorsal vertebra : but equally distinct are the met- 
apophyses which coexist with them in the seventh dorsal ; to confound these two 
processes, or to describe the longer metapophyses in the subsequent vertebrae as 
developments of the anterior zygapophyses, is to confound two things manifestly 
distinct. 
In the Dasypus sexcinctus, some modifications of the accessory processes are pre- 
sent, which render a notice of its vertebral characters desirable. 
The vertebral formula is seven cervical, eleven dorsal, three lumbar, nine sacral, 
sixteen caudal. The second and third cervicals have coalesced together, and they 
develope a strong confluent neural spine. The last four cervicals are without those 
spines, and are equally devoid of zygapophyses. The diapophysis of the last cervical 
contributes to the articular cavity for the tubercle of the first dorsal rib, which is 
enormously expanded ; and the anchylosed pleurapophysis of the seventh cervical 
projects backwards beneath the head of the first dorsal rib. The neurapophyses of 
the middle dorsal vertebrae are directly perforated for the spinal nerves, Anapo- 
* This is one of so vast a series of exceptions to the “ Loi de conjugaison ” of Prof. Serres, as to deprive 
it of any claim to be considered as the law' of formation of foramina, and to demonstrate the abuse of the term 
‘ law,’ in cases like that in which it has been made to express the idea that every foramen is formed by the 
approximation of two notches in distinct bones. 
5 c 2 
