24 
THE FIEST GREAT DIVISION. 
to check itself in this ima'^ary career, it actually effects a movement in the opposite 
<lirection. Dr Mayo describes with accuracy the phenomena attending injuries to 
the Cerebellum in various animals. “ The removal of the Cerebellum in fish produces 
no further immediate effect than that of weakening the animal; a^d frogs, from which 
this organ is removed, show an indisposition to move, unless irritated or placed in 
watei, when the movements, though less lively than before, are not observed to be 
otherwise affected. In Birds and in Mammalia, more important results ensue upon the 
injury or removal of the Cerebellum, which, it may be remarked, does not appear to 
be sensible to pain from mechanical Icsiom If the Cerebellum be wounded upon one 
side, the animal appears to be generally weakened upon the same side : if the wound 
be deep, the body upon the injured side is rendered paralytic. If, in a rabbit, the 
upper and middle portion of the Cerebellum be I’emovcd, the hind logs are observed 
to be spread, the fore logs are extended forwards in a statu of rigidity : tho whole 
attitude is that of preparation for moving backward, or throwing itself over. After 
a short time, the animal beats the ground with its fore paws, the hind legs not moving, 
and urges itself backwards. Tlie flight and walk of pigeons arc not affected by the 
removal of the upper part of the Cerebellum. After a deep section has been made, 
the bird totters, falls on its breast, rises again, and is in continual agitation. A deeper 
section still causes it to walk and fly backwards. After the entire removal of the 
Cerebellum, the bird, when irritated, walks as usual ; when thrown into the air, it 
moves its wings regularly, and lights upon its feet. M. Magendie mentions the case of 
a young woman, who was affected with a nervous malady, that forced her to run rapidly 
backwards, disregarding every peril- If, in a rabbit, a section through the middle 
jiortion of the Cerebellum be made, in the median plane, the eyes of the animal are 
obson’ed to be in extraordinary agitation, and as if starting from their sockets ; Iho 
animal inclines towards one side, then is suddenly thrown towards the opposite, as if 
unable to balance itself with precision: its fore legs are rigidly extended forwards, as if 
it were in the act of receding. If a vertical section of the Cerebellum be made, leaving 
onc-fourtb of the whole adhering to the crus (or shank) of the right side, and three- 
fourths to the left, the animal rolls over and over incessantly, turning it.self towards 
the injured side. The right eye is directed downwarils and forwards, the left eye 
upwards and backwards. On making a similar section upon the left side the animal 
stops, and the eyes resume their natural direction.” 
3. The Cerebrum, or larger lobes of the brain, arise from the expanded portions 
of the anterior or fore columns of the spinal marrow. When certain portions of the 
Cerebrum are divided in various animals, they spring suddenly forwards, and continue 
to advance steadily in a straight line. Even when opposed by some obstacle, they 
continue to preserve the attitudes of one advancing. 
4. Tho Oi’Tic Tubercles give rise to the optic nerves, and are formed by a pro- 
duction of the central columns of the spinal marrovv. Upon injuring tbi.s part of the 
brain, blindness immediately follows. 
The relative arrangement of these several parts of tho brain differs considerably 
among the several classes of animals. In Fish, they are arranged nearly in a straight 
line, while in the Mammalia and other higher tribes, they are disposed in a more com- 
plicated manner. The relative proportions also vary. In the higher animals, the 
cerebral hemispheres are much larger, in proportion to the tubercles, than in fishes. 
The Vertebrated aninuds liave always two jaws. Tlic lower jaw 
possesses tlie greatest power of motion, and may be cither raised or de- 
pressed. Tlic upper one is, in general, entirely fixed. 
The Upper jaw i.s immoveable in JIan, in QuarlmpcA,, and in some Reptiles, 
as the Tortoise and Crocodile; but it is more or less moveable in Birds, Serpents, 
and Fishes. The lower jaw is always moveable in the Ci ocodile, although the con- 
trary has been asserted. 
Bolli jaws are almost always armed witli teeth. Tliese are excrescences 
of a peculiar nature, nearly resembling bone in their chemical composi- 
tion, but wiiich grow by tlie deposition of matter in certain sacs. Yet 
one entire class of Vertebrated animals (Birds), liave tlieir jaws covered 
with a liorny substance; :md among the Reptiles, one entire genus (Tor- 
toises) are similarly supplied. 
The teeth are used by the various classes of Vertebral od animals for different pur- 
poses. In general they are for masticating the food; often for weapons of defence; 
i]i some they .arc employed for digging and for seeking out tho food; and in others, 
they seem designed fur no other purpose than for defendhig tho eyes, as in the Phaco- 
chcerus jBthiopicus, or .\friean hoar. 
The formation of teeth proceeds upon a plan entirely different from that employed 
by Nature in the deposition of bone. It will be recollected that tiie bones are per- 
vaded in every direction by vc-sseU which nourish, renovate, and absorb their particles ; 
hut the toctb, on the contrary, arc almost entirely destitute of vessels. Wiicn onco 
deposited, they remain in a cermin degree unclianged; and lienee, when ouce de- 
stroyed, they cannot he renewed. The foundations of the teeth are laid before birth, 
and each tooth is formed in a small sac, by the deposition of oartliy matter. They 
are covered by the enamel, which is tho haViicst animal substance in nature, and 
wiii even strike fire from steel. 
Tlie streehn-e of tlic teeth in graminivorous animals is peculiar. A grinder is 
composed of several di.stinct teeth, eacli tooth being covered with its own enamel, 
and tilo whole united together by a kind of cement. 
Tile int stlnul canal of the Vertebrated animals proceeds from one 
extremity of the hotly to tlie other, undergoing various bendings, with 
several expansions and contractions. It possesses subsidiary organs, and 
receives various secretions, having a dissolving power. Sonic of tliesc 
are seated in tlie mouth, and called the saliva; others, formed only 
in tlie intestines, bear several names. Tlie two most important secre- 
tions are tlie Juice formed by tiie gland called tlie Pancreas, and the Bile, 
wiiich is produced from anotlier very large gland called the Liver. 
After the food has been digested, it passes into tlie alimentary canal. 
That portion fitted for nutrition, called the chyle, is absorbed by parti- 
cular vessels called Lacieals, and transported into the veins. After the 
several parts of the body have been nourished by the blood, the nutri- 
tious particles remaining uiiabsorbed are also introduced into the veins 
by vessels analogous to the Lacteals, and forming with them an arrange- 
ment called the L^iphatic system. 
The veins bring back to the heart the blood that has served to nourish 
all parts of the body, and which has just been supplied with chyle and 
lymph. But before it is in a proper state again to be transported by fhe 
arteries throughout the body, it is obliged to pass wholly, or in part, 
through the organ of respiration. In tlie tlirce liigliest classes [Mam- 
malia, Birds, and Reptiles] tlie respiration is pulmonary, or performed 
tlirough Lungs, consisting of an assemblage of small cells through which 
the air penetrates. In the Fishes alone, and in certain Reptiles during 
the first periods of tlieir existence, tlie respiratory organ consists of 
Gills, composed of a series of tliin plates between wiiich tlie water flows. 
Ill all tile Vertebrated Animals, tlie blood supplying the liver with ma- 
terials for the bile, is derived from that venous blood which has partly 
circulated in the coats of the intestines, and partly in a particular organ 
named the Spletii. After being collected in a canal termed the Vena- 
porlm, this blood is again .subdivided at the liver. 
Tons ces auiinaiix ont aussi une secretion particiiliere, qui est celle de 
I’urine, et qui se fait dans deux grosses glandes attachecs aux cotes de 
I’epine du dos, et appelees reins: la liqueur que ces glandes produisent, 
sejourne le plus souveiit dans un reservoir appele la vessic. Les sexes 
sont separes ; la feinelle a toujours uii ou deux ovaires, d’oii les ceufs se 
detaclient au moment de la conception. Le male les fecondc jiar la li- 
queur seminalo; mais le mode de cette fecondatioii varic bcaucoup. 
Dans la plupart des genres des trois premieres classes, ellc exige une 
intromission de la liqueur ; dans quelques reptiles, ct dans la plupart dcs 
jiolssoiis, clle se fait quaiid les oeufs sont deja pondus. 
DIVISION OF THE VERTF.BllATED ANIMALS INTO FOUR CLASSES. 
1. Mammalia (Man and Beast%) — 2. Bees (Birds) 3. Beptilia (Reptiles) 
4. Risers (Fishes). 
AVe have just explained the several points in whicli all the Vertebrated 
Animals resemble each other. There are, however, certain dificrenccs, 
which give rise to their separation into four large subdivisions or classes. 
These are characterized by the particular manner in which their motions 
are peiformed, or by the degree of their energy or vigour; and these 
again depend upon the quantity of their rcspiralion. The muscular fibres 
possess a greater or less degree of irritability and general energy, according 
as the respiratory organs are more or less perfect. 
There arc two conditions which determine the quantity of Respiration. 
The first is, the relative quantity of blood supplied to the respiratory 
organ in a given time; and the second is, the relative quantity of oxygen, 
entering into tho composition of the surrounding fluid. The quantity of 
blood, purified by respiration, depends upon the arrangement of the organs 
adapted for respiration and for circnlution. 
The organ of circulation [or heart] may he either double or single. 
The entire blood, arriving from all parts of the body through the veins, 
may be obliged to circulate through the respiratory organ, before being 
again distributed by means of the arteries; this occurs when tlie heart is 
double: or a part only of tho blood returning from the body may be 
obliged to traverse the respiratory organ, while the remainder returns 
through the liody, without having been submitted to the action of respira- 
tion— which is the case wlieii the heart is single. The latter arrangement 
occurs in Reptiles; and the quantity of their res[)iration, with all tlie 
qualities depending tlicreoii, is determined by the quantity of the blood 
transmitted to the lungs at each pulsation. 
Tlie circulation of the w.ann-biootlcd animals, possessed of a doable lieart [being 
Wammalia and Birds] is performed in the following manner: — The blood is propellr'* 
from the left ventricle into the aorta, and fhonce diifnsed tliroughout the body by 
means of the arteries. It passes tlirough tho minute capillary vessels at the extremities 
of the ai'teries into the veins ; from wiiich it slowly collects in the vena cava, and i» 
deposited in the right auricle of tlic lieart, and thence removed into the right ventricle. 
It is then propelled by tlie right ventricle througii the pulmonary ai*tery into the lungs, 
where it receives tlie action of tho air ; and being restored by tlie pulmonary veins back 
again to tlie left anriele of tlie heart, it passes thence into tho left ventricle, prepa‘V'1 
again to resume its circuitous coui'se. 
Tho force exercised by the heart upon the blood, and the velocity of the circulation. 
