ZOOLOGY, 
827 
the repository of fluid, over which the vertebrae turn, as on a 
pivot, while they are supported by the elasticity of the cartila¬ 
ginous edges. 
The third of the structures mentioned by Home, i what 
is met with in all the members of the mammalia. They are 
weak in proportion to their extent of movement, are strength¬ 
ened by ligaments in part, but still more by muscles. 
We shall postpone any general view of the nervous and 
sentient systems, until we speak of them in detail; because, 
having, with regard to their functions, some peculiar views 
to offer, it will be more convenient to refer immediately to 
the facts on which these are founded. 
Classification. 
The arrangement of animals into the most convenient or¬ 
der for description, is generally allowed to be a task of the 
greatest difficulty. It has employed many of the ablest zoo¬ 
logists, but is at present far from satisfactory. The classifi¬ 
cation of Linnseus, (see Natural History,) which we 
have adhered to throughout this work, is not well calculated 
for the ready display of zootomical facts. But we have 
adopted the system of Blumenbach, which being only a slight 
modification of the former, will best enable our readers to 
connect this article with the descriptions of the different 
genera dispersed throughout this work. We have thought 
proper to add, however, the arrangement of Cuvier, as one 
very generally adopted, and, for comparative anatomy, supe¬ 
rior to that of Linnseus. We copy with little alteration, the 
following exposition of these systems, from Mr. Lawrence’s 
introduction to Blumenbach’s manual of anatomy, which in¬ 
estimable work, it is proper to acknowledge, we have made, 
in considerable portions of the rest of this article, our text¬ 
book. 
The differences of structure in the organs of circulation of 
such animals as possess a cardiac system, indicate the follow¬ 
ing classification. 
i. T ,■ . . C Heart furnished with two 
Mammalia, viviparous . 
Birds, oviparous. 
ventricles, two auricles; 
blood warm and red. 
. ,. -'ii f Heart furnished with one 
Amphibia, respiring by lungs.. J vpntHrlp nnH 
nnfi anri. 
lushes, breathing by gills .. 
•i 
Insects, furnished with antennae j Sanies 
Vermes ,furnished with tentacula\ less. 
ventricle and one auri¬ 
cle; blood cold and red. 
cold and colour- 
Animals may be divided into two great families; the first 
family possessing vertebrae, and red blood ; the second with¬ 
out vertebrae, and most of them with white blood. The 
former have always an internal articulated skeleton, of which 
the chief connecting part is the vertebral column. The ante¬ 
rior part of this column supports the head ; the canal, which 
passes from one end of it to the other, incloses the common 
fasciculus of the nerves; its posterior extremity is most fre¬ 
quently prolonged, in order to form the tail, and its sides 
are articulated with the ribs, which are seldom wanting. 
None of this family of animals has more than four limbs, 
some of them have two only, and others have none. 
The brain is inclosed in a particular osseous cavity of the 
head, called the cranium. All the nerves of the spine con¬ 
tribute filaments to form a nervous cord, which has its origin 
in the nerves of the cranium, and is distributed to the greater 
part of the viscera. 
The senses are always five in number. There are always 
two eyes, moveable at pleasure. The ear has always at least 
three semicircular canals. The sense of smell is alway scon- 
fined to particular cavities in the fore part of the head. 
The circulation is always performed by one fleshy ven¬ 
tricle at least; and where the ventricles are two in number, 
they are always close together, forming a single mass. The 
absorbent vessels are distinct from the sanguilerous veins. 
The two jaws are always placed horizontally, and open 
from above downwards. The intestinal canal is continued 
without interruption, from the mouth to the anus, which is 
always placed behind (lie pelvis, that is, behind the circle of 
.bones which affords a fixed point for the posterior extremi¬ 
ties. The intestines are enveloped within a membranous 
sac, termed peritonaeum. There is always a liver and a pan¬ 
creas, which pour their secretions into the cavity of the intes¬ 
tines; and there is always a spleen, within which part of the 
blood undergoes some preparatory change before it is sent to 
the liver. 
There are always two kidneys for the secretion of urine, 
placed on the two sides of the spine, and without the perito¬ 
naeum. The testicles also are always two in number. There 
are always two bodies, called atrabiliary capsules, placed over 
the kidneys; the use of them is unknown. 
Animals with vertebrae are subdivided into two classes, 
one of which is warm-blooded, and the other cold-blooded. 
Warm-blooded vertebrated animals have always two ven¬ 
tricles, and a double circulation. They respire by means of 
lungs, and cannot exist without respiration. The brain al¬ 
most always fills the cavity of the cranium. The eyes are 
covered with eyelids. The tympanum of the ear is sunk 
within the cranium; the different parts of the labyrinth are 
completely inclosed within bone; and, besides the semicir¬ 
cular canals, the labyrinth contains the cochlea, with two 
scales, resembling the shell of the snail. The nostrils al¬ 
ways communicate with the throat, aud afford a passage for 
the air in respiration. The trunk is furnished with ribs, and 
almost all the species of this branch of animals have four 
limbs. 
Cold-blooded vertebrated animals resemble one another 
more by their negative than their positive characters. Many 
of them are destitute of ribs; some of them are totally des¬ 
titute of limbs. The brain never fills the whole cavity of 
the cranium. The eyes seldom have moveable eyelids. The 
tympanum of the ear, when present, is always close to the 
surface of the head; it is often absent, as are likewise the 
ossicula auditus; the cochlea is always wanting. The diffe¬ 
rent parts of the ear are not firmly attached to the cranium; 
they are often loosely connected to it in the same cavity as 
the brain. 
Each of these two branches is subdivided into two classes. 
The two classes of warm-blooded animals are the Mam¬ 
malia and Birds. 
The Mammalia are viviparous, and suckle their young 
with milk secreted by the mammae. The females have con¬ 
sequently always the cavity termed uterus, with two cornua, 
and the males have always a penis. 
The head is supported on the first vertebrae by two emi¬ 
nences. The vertebrae of the neck are never less than six, 
nor more than nine. The brain has a more complicated 
structure than in other animals, and contains many parts 
which are not to be found in the other classes, such as the 
corpus callosum, fornix, pons, &c. 
The eyes have two eyelids only. The ear contains four 
small bones, articulated together, and has a spiral cochlea. 
The tongue is quite soft and fleshy. The skin is covered 
entirely with hairs, in the greatest number, and in all it is co¬ 
vered partially. 
The lungs fill the cavity of the chest, which is separated 
from the abdomen by a fleshy diaphragm. 
There is one larynx only, situated at the basis of the tongue, 
and completely covered by the epiglottis, when the animal 
swallows. 
The lower jaw only is moveable; both jaws are covered 
with lips. 
The biliary and pancreatic ducts are inserted into the in¬ 
testinal canal at the same place. The lacteal vessels convey 
a white milky chyle, and pass through a number of conglo¬ 
bate glands, situated at the mesentery. A membrane, called 
omentum, suspended from the stomach and adjacent viscera, 
covers the fore part of the intestines. The spleen is always 
upon the left side, between the stomach, ribs, and diaphragm. 
Blumenbach establishes the following orders in this class : 
Order I. Bimanus, two-handed. Genus, Homo. 
Order II. Quadrumana, four-handed animals: having a 
separate thumb capable of being opposed to the other fingers, 
both in their upper and lower extremities, teeth like those of 
man, except that the cuspidati are generally longer.—1. 
Simiae, apes, monkeys, baboons.—2. Lemur, macauco. 
Order 
