PROFESSOR OWEN ON THE MEGATHERIUM. 
739 
in the fourth (Plate XLVIIL, fig. 15 , d 4), and is gradually transferred in the sixth 
(d e) and seventh (u 7) dorsals to the outer side of the prozygapophyses (2) : in the fol- 
lowing vertebrae it seems to take their place, and to occasion a reversing of the usual 
relative position of the zygapophysis ; for whereas in the cervical and anterior dorsal 
vertebrae the anterior zygapophyses are overlapped, as in other mammals, by the 
posterior zygapophyses, in the succeeding dorsals, beginning with the seventh, the 
posterior zygapophyses seem to be overlapped and concealed by the anterior zygapo- 
physis. But this is not the case ; the appearance is due to the place of the prozyg- 
apophyses (2) being taken by the metapophyses (m). These latter processes, in fact, 
continue after the articular surface has ceased to be developed, and after the entire 
disappearance of the posterior zygapophyses, to project forwards from the thirteenth 
dorsal to the sixth lumbar vertebra inclusive ; beyond which the neural arch is devoid 
of all exogenous processes, save the spine, until the middle caudal vertebrae, where 
rudiments of the metapophyses again reappear. 
In the common Dolphin {Delphinus Delphis), Plate XLVIII. fig. 16 , the metapo- 
physis (m) begins abruptly, as a long well-marked process, from the fore-part of the 
diapophysis (d) of the fourth dorsal (d 4) ; progressively approximates and attains the 
outside of the prozygapophysis in the eighth dorsal (d s), performs the function of an 
articular process as far as the sixth lumbar, clamping, as it were, the sides of the 
back part of the base of the spine of the antecedent vertebra, disappears in the next 
dozen lumbar vertebrae, and reappears in the caudal vertebrae at the fore-part of the 
base of the spine. 
There are no anapophyses in the Cetacea. With respect to the metapophyses, 
Cuvier, in his description of the vertebrae of the Dolphin, confounds them, as Straus- 
Durckheim has done in the Cat, with the true zygapophyses. He writes, — “ The 
last cervical and the six first dorsals have their articular processes joined together by 
horizontal facets, of which the anterior looks upwards. At the sixth they begin to 
be oblique, at the seventh they are nearly vertical, the anterior looking inwards^.” 
But in the figure which he refers to, of the fourth dorsal vertebra of the Delphinus 
Delphis, the accurate artist, M. Laurillard, represents the metapophyses as distinct 
from the prozygapophysis or anterior articular process, although less so than it is in 
nature; and it is incontestably the progressive development of this superadded pro- 
cess which gives rise to the change of position of the articular surface of the connate 
prozygapophysis : and the metapophysis continues to be developed, as the figures in 
the ‘Ossemens Fossiles’ demonstrate, long after the articular process or any articular- 
surface has ceased to exist'|~. 
* Ossemens Fossiles, Ed. 1823, tom. v. pt. i. p. 303, pi. xxiii. figs. 25 — 29. 
i‘ This fact is clearly recognized by Professor Stannius, in his ‘ Vergleichende Anatomic der Wirbelthiere,’ 
8vo., p. 345, where he describes the ‘metapophyses’ as ‘processus accessorii.’ 
