Encyclopaedia Britannica, or, a Dictionary of arts, sciences, and miscellaneous literature : enlarged and improved. Illustrated with nearly six hundred engravings > Volume 8, ELE-FOR

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Anatomy,
ternum.
pint.
ect.
:apula.
II. E R P E T
, rlbs are articulated with one vertebra only; but in the
; ftruflure and articulations of thefe bones there is a pe¬
culiarity in the crocodile and chameleon. The two
firft and the two laft ribs of the crocodile do not termi¬
nate in the fternum. The cartilages which attach the
other eight are broken, fo that each rib from the verte¬
bra to the fternum is compofed of three parts, one of
which is bony, the other two cartilaginous. In the
chameleon the two firft anterior ribs are not fupported
by the fternum ; the four following are attached to it
by means of appendages which form at the point of
jun&ion an angle with the ribs, and which are not
compofed of a fubftance purely cartilaginous, but as
hard as that of the ribs. The 10 other following ribs
do not reach the fternum. Each is joined to that which
is oppofed to it by a bony appendage, forming an arch
on the middle of the thorax and abdomen. The three
laft are loofe, feparated, and as it wrere truncated in the
middle.
The fternum or breaft bone is a flat bone, placed on
the anterior part of the thorax,, the figure and dimen-
fions of which vary confiderably. In the crocodile
this bone reaches to the third rib ; it is compofed of a
fingle piece, having at its upper part a kind of carti¬
lage which forms a point towards the throat, and which
enlarging at the fides covers the clavicles. The fternum
of the chameleon and the frog is compofed of four
bones, the firft of which is very large.
The back bone comprehends the vertebras which
occupy the upper part of the back, including thofe of
the loins. In the chameleon there are 22; in the cro¬
codile 19, and in the gray lizard 22.
The vertebrae of the tail form the pofterior extremi¬
ty of the fpiral column. Their number is always pro¬
portional to its length. The tail of the chameleon is
furniftied with i;o vertebrae ; that of the crocodile 33,
and that of the gray lizard 60. All thefe vertebrae
are furnifhed with tranfverfe,. oblique, and fpinous pro-
cefles, excepting thofe towards the end of the tail,
which are ufually dettitute of the oblique proceffes.
The bones of the feet bear a conliderable refem-
blance to thofe of other animals. The fore feet are
eompofed of the fcapula, the humerus, the cubitus and
radius, the bones of the carpus and metacarpus, and
the joints of the toes.
The fcapula or fhoulder-blade is fometimes fingle,
and fometimes double, in the animals belonging to this
order. The frog, the chameleon, and the falamander,
have only one; but it is of fuch a length that it ex¬
tends from the dorfal fpine to the fternum, w ith which
it is articulated, anfwering the purpofe of a clavicle.
In the tortoifes and crocodile, there are twm fhoulder-
blades, viz. one on the back, and one placed anteriorly,
and articulated with the fternum. Thefe alio perform
the funclions of the clavicle. The humerus is articu¬
lated on the one hand with the fcapula, and with the
two bones, the cubitus and radius of the arm, on the
other. The two latter bones, the cubitus and radius,
are placed parallel to each other, between the humerus
and the bones of the carpus and metacarpus. Thefe
latter are fituated between the two bones of the fore¬
arm, and the phalanges or joints of the toes.
The hind feet are compofed alfo of the femur or
thigh-bone, the tibia, and the peronea of the leg ; the
bones of the tarfus and metatarfus, and the phalanges
O L O G Y. 309
or joints of the toes. Thefe, excepting that they differ Anatomy,
fomewhat in ftrufture, bear fo near a refemblance to 1
thofe of the fore feet, that it w'ould be quite unnecef-
fary to enumerate or defcribe them particularly.
2. The Muscles.—The mufcles are the inftruments Mufcles of
of motion. The mufcles of the back of the crocodile the back,
take their origin from the vertebrse and ribs, and they
are attached by means of their tendons, to the bands
or rings which are formed by the tubercles of the
back. Thefe tendons act in different, directions; fome
of them pull thefe bands from above downwards, w-hile
others pull them from below upwards. The ufe of
thefe mufcles is apparently to lock together more
ftrongly the rings of which the tubercles of the back
are compofed.
The mufcles of the abdomen in the fame animal, Of the ab~
which are four in number, one external, and one in- domen.
ternal on each fide, are not only different from thofe of
other quadrupeds in number, but alfo in their fituation
and ftrufture. The external mufcle is placed upon the
ribs, and the internal under them, immediately above
all the vifcera, which it embraces in the manner of a
peritoneum. The internal mufcle is attached on one
fide to the bones of the pelvis, and to the tranfverfe
proceffes of the lumbar vertebras ; and on the other it -
terminates in a broad tendon, which envelopes all the
inteftines in the form of a membrane.. The fibres of
thefe two mufcles are difpofed lengthwife.
3. The Viscera.—The parts contained in the three
great cavities of the body are the vifcera. Thefe are
the brain, the heart, the lungs, the ftomach, the intef¬
tines, the liver, the fpleen, and the kidneys.
The brain is fituated within the cavity of the fkull. Brain.
This organ, in reptiles, is in general of fmall fize. The
brain of the chameleon, which is of a reddifhor grayifti
red colour, is not more than a line in diameter. The
fame organ in the crocodile is very fmall, andfimilar to
that of fifties. The cavity within which it is contained,,
does not exceed 14, lines in length, and about 12 in
breadth and depth.
The heart is a ftrong mufcular body, from which pro- Heart,
ceed the great arteries, and in which the great veins
terminate. From the contraftile force of this organ,
the blood receives its firft impulfe. The heart in this
order of animals is fmall.. It has in general been con-
fidered as having only one ventricle and two auricles ;
differing from the heart of the more perfect animals,
which is furniftied wdth two ventricles and tw'o auricles..,
But from the obfervations of later naturalifts, it would
appear that the ftrufture of the heart of reptiles has not
been accurately defcribed ; for, according to fome ana-
tomifts and phyfiologifts, the heart of this order of ani¬
mals is really double ; that is, confifting of two au¬
ricles which have a diredt communication with each
other, and two ventricles, as in other animals.
'T he lungs which conftitute the principal organ of Lungs,
refpiration, are fpongy cellular bodies, in which the
bronchia or air-veffels are ramified. The fubftance of
which the lungs of reptiles are compofed, is not fielhy
and parenchymatous like thofe of quadrupeds, but they
confift of a bundle of veficles divided into tw'o lobes.
The lungs of the turtle are remarkable for a veficle
which adheres to their furface on the left fide, and
which may be contradted and dilated at the pleafure of
the animal. It is conjedlured, that it is by means of
this;