858 
these osseous masses are generally small, and 
sometimes without material density, the indi- 
vidual granules not having firmly united. In 
8 they resemble in every point adventitious 
ne. 
If in a young animal the fracture be not 
kept tolerably quiet, the motion between the 
fractured bone will prevent the formation of 
cartilage, which seems necessary to the deve- 
lopement of bone, and here, therefore, osseous 
masses will alone present themselves. This 
fact is very interesting in a surgical point of 
view, and might be treated more at length ; but 
having given a detailed account of the deve- 
lopement of bone and of the distinction to be 
made between true bone and adventitious 
osseous tissue, I shall conclude the article. 
(J. Tomes.) 
OVARY.—See Supprement. 
OVUM.—See Suprremenrt. 
PACHYDERMATA.—An extensive group 
of herbivorous quadrupeds, constituting a dis- 
tinct order of the class Mammalia, generally 
remarkable for their ponderous bulk and un- 
wieldy appearance, and seemingly forming the 
transition between the gigantic Cetacea, which 
from their size are only adapted to an aquatic 
existence, and the vegetable-eating Mammals 
of strictly terrestrial habits. Even the localities 
where they are met with would seem to indi- 
cate that they constitute such a connecting 
link, seeing that their most typical forms are 
peculiarly adapted to be occupants of the river 
and the marsh, from the Hippopotamus, that 
5a aQVe 
of ee > > 
PACHYDERMATA. 
Sheleton of Elephant ( Elephas Indicus ). 
might almost be considered an aquatie ani 
to the Tapirs and the Hog, which still ore 
wallow in mud although they approximate in 
their habits to the ruminatin undreaae At 
the present day the order Pachydermata con- 
tains but few genera, and these for the most 
x embrace a very limited number of species. 
ut in former periods of the history of our 
globe they must have existed under much — 
greater variety of form, seeing that the tertiary 
deposits yield to the geologist, in abundance, 
the remains of iM humerous genera now 
totally extinct, to the list of which modern 
researches are adding day by day; it is indeed 
more than probable that many of the existing 
races will ily perish, for the hand of man 
is against them, and the bullet and the pear 
are doing their work of extermination rapidly, 
so that the Tapir and the Elephant, like the 
Palcotherium and the Mastodon, may soon be 
classified with extinct existences. 
The order of Mammalia under consideration 
is usually divided into Prososcrprans, in- 
cluding such Pachydermata as are provided 
with a proboscis and tusks, of which the Ele 
hant is the only existing example, and into 
RDINARY PacHyDERMATA, which are unpro- 
vided with a proboscis, and characterized by 
possessing four, three, or two large digits or 
their feet, which are cased in horny hoof 
last group being distinguishable from the Run 
nantia by the simple construction of thei 
stomachs, although closely approaching them 
in many points of their economy. The abor 
division, however useful to the zoologist, i 
nevertheless by no means based on n 
proboscis of the Elephant being onlya maximur 
‘ 
) 
~ 
