O P H 



[ 188] 



ORB 



them as if running on all fours, pursuing 

 their prey, rapidly winding through the 

 turf, and through the low vegetables tha 

 cover extensive plains. If the prey, t< 

 escape from danger, betake itself to thi 

 trees, imagining there to be in safety, w< 

 find these serpents winding round the 

 tree, and almost without any apparen 

 motion of any portion of their trunk 

 gliding, as if they were sticking by suck- 

 ers to the trunks of the trees they climb 

 till within reach, and then with a velo- 

 city, like an elastic spring let loose 

 they dart forward and twine rounc 

 their prey. If their prey should even rise 

 from the ground into the air, we see these 

 serpents, as if they were gifted with wings 

 spring with velocity from the ground, dart 

 upon the bird and seize it, or if the ani- 

 mal be a quadruped, and plunge for 

 safety into the water, the serpents still 

 pursue them in that element, swimming 

 like fishes. Yet, when we examine the 

 condition of the skeleton, we find it 

 simply to consist of a vertebral column 

 and ribs ; and with that simple condition 

 of the solid internal frame-work, we see 

 all those varied movements effected. The 

 spine of serpents is formed of a great 

 number of vertebrae ; in the rattle-snake 

 there are about two hundred, and in the 

 coluber natrix above three hundred have 

 been counted. These vertebras are all 

 united by ball and socket joints, the pos- 

 terior rounded eminence of each vertebra 

 being received into the anterior surface of 

 the next. Serpents swallow their prey 

 entire ; and it is well ascertained that 

 they will swallow animals having ten times 

 the diameter of that of their own neck. 

 The loose connexion of all the bones 

 surrounding the mouth of serpents, en- 

 ables them to distend their jaws and 

 mouth to receive undivided prey, and 

 thus, so far as food is concerned, to dis- 

 pense with arms to grasp it, and assist in 

 its sub-divisiou. Neither are their teeth 

 suited for mastication, being conical, 

 slender, sharp, osseous, and recurved. 



Venomous serpents, or those with iso- 

 lated fangs, have their organs of mandu- 

 cation constructed on a very peculiar plan. 

 Their superior maxillary bones are very 

 small, attached to a long pedicle, and are 

 very moveable ; in them is fixed a sharp - 

 pointed pervious tooth, through which 

 flows a liquor which, poured into the 

 wound made by the tooth, produces 

 effects according to the species of the 

 reptile secreting it. This tooth, when 

 the animal does not wish to use it, is con- 

 cealed in a fold of the gum, and behind it 

 are several germs destined to replace it, 

 in the event of its being broken. 



All those venomous serpents, whose 



mode of production is well ascertained, 

 bring forth living young ones, as their 

 eggs are hatched without being laid. 

 Grant. M'Murtrie. Royet. 

 OPHI'DIOUS. Belonging to the order 



Ophidia. . 



OPHI'OLITE. (from o<pig, a serpent, and 

 \<0o, a stone, Gr.) Another name for 

 the mineral serpentine. 

 O'PHITE. (O^J'TTJC, lapis in modum serpen- 

 tis maculosus, ab o$>i, a serpent, Gr.) 

 Green porphyry, or serpentine. A green- 

 stone, varying from blackish-green to 

 pistachio-green. It contains greenish- 

 white crystals of felspar, which on the 

 polished surface often shew themselves in 

 parallelograms, and are sometimes cru- 

 ciform. It occurs massive and disse- 

 minated. Lustre glistening and resinous. 

 Fracture conchoidal, and often splin- 

 tery. 



OPO'SSUM. A genus of quadrupeds belong- 

 ing to the order Marsupialia. The opos- 

 sums are peculiar to America, and are 

 remarkable for having a greater number 

 of teeth than any other animal, amounting 

 in all to fifty. These teeth are thus di- 

 vided : ten incisors above and eight below, 

 three anterior compressed grinders, and 

 four posterior bristled ones, which with 

 the four canine make the fifty. They 

 approach the quadrumanes, by having the 

 thumb of their hind foot opposed to the 

 fingers, whence they have been called 

 pedimanes : the thumb is not armed with 

 a nail. 



The small opossums, in the oolite for- 

 mation at Stonesfield, are the only land 

 mammalia whose bones have yet been 

 discovered in any strata more ancient 

 than the tertiary. 



O'PPOSITE. (oppositus, Lat.) In botany, 

 applied to the position of leaves placed 

 exactly opposite each other on the stem ; 

 also to b'ranches growing in pairs ; and to 

 peduncles placed opposite to a leaf. 

 Flora Medica. 



O'PTICS. (from oTrrojuai, to see, Gr.) 



That branch of science which treats of 



the properties of light and of vision, as 



performed by the human eye. 



O'RBED. Round ; circular ; formed in a 



circle. 



ORBI'CULA. (from orbis, an orb, Lat.) A 

 genus of bivalve shells belonging to the 

 family Brachiopoda. The orbicula is a 

 very small inequivalved flat bivalve ; the 

 lower valve very thin and adherent to 

 other bodies. It is a marine shell, found 

 at depths varying to sixteen fathoms, 

 attached to stones, shells, sunken wrecks, 

 &c. Orbicula? have not been found 

 fossil. 



ORBI'CULAR. (orbiculaire, Fr. orbicolare, 

 It.) Spherical; circular; roundish and 



