PROFESSOR OWEN ON THE MEGATHERIUM. 
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lost forms of animal life, I found that a very large proportion of their fossil remains 
consisted of vertebrae or parts of vertebrae, and that a definite idea of these complex 
bones, with a substantive nomenclature for their parts, was indispensable in order to 
give a clear and intelligible description of them. In a memoir on the Plesiosaurus 
macrocephalus read before the Geological Society, April 1838, I therefore defined the 
parts of the typical vertebra, distinguished the autogenous elements from the 
exogenous parts, and proposed the nomenclature which I have since used and further- 
illustrated in subsequent works. Referring more particularly to my ‘Lectures on 
the Comparative Anatomy of the Vertebi-ate Animals*,’ and my work ‘On the 
Archetype of the Vertebi-ate Skeleton-f-,’ for the fuller exposition of the views 
entertained by anatomists on the nature of the vertebra, it is sufficient for the present 
purpose to remark, that the term ‘ parapophysis’ was proposed for the ‘inferior 
transverse process,’ or ‘ anterior root of the perforated transverse process of the cer- 
vical vertebrae’; the term ‘diapophysis’ for the ‘superior transverse process,’ or 
‘ posterior root of the perforated transverse process’ ; and the term ‘ pleurapophysis ’ 
for that element, which, essentially the same in different regions of the spine, is short, 
styliform, and speedily anchylosed in the neck of Man, is remarkable for its length 
and freedom of motion in the back, and is as remarkable for its breadth, thickness, 
and wedged fixedness in the sacrum ; which is hatchet-shaped and free in the neck 
of the Crocodile and Plesiosaurus ; and is as broad and flat, in the first dorsal seg- 
ment of a Whale, as the ordinary mammalian scapula or any of the ‘flat bones’ in 
Anthropotomy. 
The necessity for a definite technical term for this vertebral element was the 
greater because the name ‘ costa’ or ‘ rib’ has not only been withheld in Human 
Anatomy from the element in question, under every modification save that in which it 
retains its individuality and mobility with a certain length and slenderness ; but it has 
been extended to another and quite distinct element, viz. the ‘ hsemapophysis,’ which 
from being commonly cartilaginous in the thorax of Man, has obtained the name of 
‘cartilage of the rib,’ or ‘ pars cartilaginea costee.’ As this part however is most 
commonly a distinct ossified part in the air-breathing Vertebrata, it has been called 
in Comparative Anatomy the ‘ sternal rib,’ in contradistinction to the ‘ vertebral 
rib’ or ‘pars ossea costae’ of Anthropotomy. Both, however, are distinct elements 
of the ‘ vertebra’ in its true or wider anatomical sense ; each may exist independ- 
ently of the other, and the haemapophysis is often present in other regions besides 
the sternal or thoracic one. 
The subject, however, of the present communication being the ‘ exogenous parts 
of the vertebrae,’ I shall return to it by remarking, that, in Human Anatomy, other 
processes have been recognized besides the ‘spine,’ the ‘ zygapophysis’ (oblique or 
articular process), the ‘diapophysis’ (transverse process and ‘radix postica’ in the 
neck) and the ‘parapophysis’ (part of the ‘radix antica’ in the neck). Monro, for 
* 8vo. Longmans, 1846. 
t 8vo. Van Voorst, 1848. 
