Olio 
wliidi is situated along the middle of the os 
frontis, and the ossa bregmatis. The man- 
dible of this animal consists of a beak, the 
nnder part of which has its margin indented 
as in ducks, and of the proper instrument 
for chewing that is situated behind, within 
the cheeks^ Dr. Shaw says it has no teeth, 
though Mr. Home found, in a specimen ex- 
amined by him, two small and flat molar 
teetli on each side of the jaws. Ihe tore- 
part of this mandible, or beak, is covered 
and bordered with a coriaceous skin, in 
which three parts are to be distinguished, 
viz. the proper, integument of the beak; 
the labiateil margins of it ; and a curious 
edge of the skin of the beak. Into these 
three parts of that membrane numerous 
nerves are distributed, intended, probably, 
as the organs of feeling, a sense which, be- 
sides men, few mammalia enjoy ; that is, 
few animals possess the faculty of distin- 
guishing the form of external objects, and 
their qualities, by organs destined for that 
purpose, a property very ditferent from the 
common feeling by which every animal is 
able to perceive the temperature and pre- 
sence of sensible objects, but without be- 
ing informed by the touch of them, of their 
peculiar qualities. Thus the skin in the 
wings of the bat, and its ear, are supposed 
the organs of common feeling, by means of 
which they are enabled to flutter, after be- 
in<r blinded, without flying against any 
thing. The whiskers of many animals ap- 
pear likewise to serve the same purpose of 
informing them of the presence of sensible 
bodies, and hence they have been com- 
pared to the antennae of insects. But to 
return to the ornithorhynchus : it is an am- 
mal which, from the similarity of its abode, 
and the manner of searching for food, agrees 
much with the duck, on which account it 
has been provided with an organ for touch- 
in-r, viz. with the integument of the beak 
richly endowed with nerves. This instance 
of analogy in the structure of a singular or- 
gan of sense in two species of animals, from 
classes quite different, is a most curious cir- 
cumstance in comparative physiology, and 
hence the ornithorhynchus is looked upon 
as one of the most remarkable phenomena 
of zoology. 
OROBANCHE, in botany, broom-rape, 
a •'enus of the Didynamia Angiospermia 
ctess and order. Natural order ofPerson- 
at®. Pediculares, Jussieu. Essential cha- 
racter: calyx bifid; corolla ringent; cap- 
sule one-celled, two-valved, many-seeded ; 
gland under the base of the germ. There 
aie fourteen species. 
ORT 
OROBUS, in botany, hitler vetch, a ge- 
nus of the Diadelphia Decandria class and 
order. Natural order of Papilionace®, or 
Leguminos®. Essential character ; calyx 
blunt at the base ; the upper teeth deeper 
and shorter; style linear. There are six- 
teen species. 
ORONTIUM, in botany, a genus of the 
Hexandria Monogynia class and ordei . Na- 
tural order of Piperit®. Aroide®, Jussieu. 
Essential character ; spadix cylindrical, co- 
vered with florets ; corolla six-petalled, na- 
ked ; style none ; follicles one-seeded. 
There are two species, fis. O. aquaticum, 
and O. japonicum. 
ORPHAN. In tlie city of London there 
is a court of record established for the care 
and government of orphans. 
ORPIMENT is a fine yellow powder, 
formed from a solution of the white oxide 
of arsenic in muriatic acid, to which is add- 
ed a solution of sulphuretted hydrogen in 
water. It may also be obtained by sub- 
liming arsenic and sulphur by a heat not 
sufficient to melt them. It is likewise 
found native in many parts of Germany and 
Italy, composed of plates that have a consi- 
derable degree of flexibility. Its specific 
gravity is .5.3. It is used as a pigment. 
The Chinese fashion vessels of different 
shapes, and their pagodas, of tlje mineral. 
ORRERY, a curious machine for repre- 
senting the motions and appearances of the 
heavenly bodies. See Planetariujm. 
ORTEGIA, in botany, so named in ho- 
nour of Joseph Ortega ; a genus of the Tri- 
andria Monogynia class and order. Natu- 
ral order of Caryophylle®. Essential cha- 
racter : calyx five-leaved ; corolla none ; 
capsule one-celled; seeds very many. 
There are two species, viz. O. Hispanica, 
Spanish ortegia, and O. dichotoma, forked 
ortegia, natives of Spain and Italy. 
ORTHOGR-APHIC projection of the 
sphere, that wherein the eye is supposed at 
an infinite distance; so called because the 
perpendiculars from any point of the sphere 
will all fall in the common intersection of 
the sphere with the plane of the projec- 
tion. 
ORTHOGRAPHY, that part of gram- 
mar which teaches the nature and affections 
of letters, and the just metliod of spelling 
or writing words with all the proper and 
necessary letters, making one of the foil, 
greatest divisions or branches of grammar. 
Orthography, in geometry, the art or 
drawing or delineating the fore right plan 
of any object, and of expressing the heights 
or elevations of each part. It is called or- 
