22 
THE FIRST GREAT DIVISION. 
Tlie Reverend Mr. V.'assc found that several persons, enlisted as soldiers in the 
morning, bad been discharged for want of height, on their being measured again before 
the officers in the evening. On this occasion, he measured several other persons at 
different times, and found that the variation, in many cases, was wot less than an inch. 
This gentleman observed, from his own personal experience, that on fixing a bar of 
iron, which he Just reached with his head on getting out of bed in the morning, he 
would nearly want half an inch of his height in an hour or less, if he employed the 
time in rolling his garden walks, or any other exercise of tho laborious kind, lie 
also observed that the height was very suddenly diminished by riding; and, what 
appeared remarkable, he found that on sitting almost motionless in his study for several 
hours he often lost a w’hole inch of his height. 
It appears evident that this cliange is occasioned merely by the back bone, from 
the circumstance tliat it arises in persons when they sit as well as when they stand. 
The structure of this part of the body is beautifully adapted to the several purposes 
for which it was intended in the several tribes of animals, and in none more so tlian 
in Man. By the thickness and shortness of the several vertebral, and by the inter- 
vening cartilages, with the bony projections, it is adapted for motions peculiar to itself. 
Had the several vertebra been of any considerable length, the articulations must have 
inclined at a large angle upon their innermost edges, and the spinal marrow within 
the bones would have been continually liable to injury. Again, if the cartilages had 
been entirely wanting, it would have been as useless as if it w'crc but one bone, and 
then the body would have been rendered incapable of bending, and would have remained 
for ever in an erect posture. The remarkable differences among the cai'tilages of the 
three kinds of vertebral are other singular instances of exquisite arrangement. 
The vertebrae of the back require but liUle motion; and the cartilages in that part 
of tlic column arc small and thin when compared with those of the loins. In this 
latter part, the motion is much greater, and being placed lowest, it also supports a 
gi-eater weight. It therefore follows, that during the period of the day in which wo 
arc actively engaged in the several duties of life, until wo dispose ourselves for rest, 
the cartilages of the spine will become more close and compact from the pressure they 
sustain : and consequently, the whole spine, which alone supports the body, will become 
shorter. On the contrary, when this superior weight is entirely removed, by placing 
the body in tho horizontal position, as it always is when wo ai’o in bed, the compressed 
cartilages will begin to enlarge themselves, until they gradually recover their expanded 
state. 
As the cartilages between the several vertebr® arc twordy-four in number, and as 
every one of these is pressed in our daily employments, the aggregate of their several 
expansions cannot be supposed less than an inch. This pressure is occasioned by tho 
weight the body alone upon the spinal column ; it must therefore be much greater in 
persons constantly emf)loyed in carrying bui'dens. That the compression and expansion 
of the cartilages in older people is less tlian in younger, is a necessary consequence 
of the cartilages gro-wlng harder in tho course of time, and becoming less capable of 
compression. It also follows, that old persons must lose some part of their former 
height, from the cartilages shrinking into a smaller compass as they grow bony; and 
this shortening, or “growing dowmwards,” is not imaginary, as persous conunonly 
suppose, but a real phenomenon. 
In general, the spine is prolonged into a tail, extending beyond the lower 
extremities. 
Man possesses a kind of vudimcntal tail, in the os coccyyis, terminating the spinal 
column. Among Mammalia, the Ternate Bats alone are destitute of this rudimcntal 
tail; it is wanting altogether in the Batrachia or Frog tribe. 
The ribs may be compared to semi-circular hoops, tvhich protect the 
sides of the cavity of the trunk. They are articulated at one extremity 
to the vertebrte, and generally the other end is fixed to the sternum or 
breast bone ; but frequently they do not enclose the entire trunk, and 
there are some species in which they arc scarcely visible. 
The vertebra; arc never entirely wanting, although thoir number is exceedingly 
variable. Those which sustain the ribs are called dorsal; those between tho dorsal 
and the head are tomed cerdcul; those below the dorsal, luinbar; those connected 
with the pelvis, or hinder extremity, sacral or pcloic; and those forming the tail, 
coccygeal or caudal. Tlic ribs are wanting in Frogs, also in Rays, »Shark.s, and a 
great nurribor of cartilaginous Fishes. It is obvious that in the animals without ribs, 
the distinction of the throe first kinds of vertebr® cannot take place, and th.it tho 
distinction of the three last disappears in those having no hinder limbs, or where their 
limbs arc not attached to tho spine. 
Tim ribs which proceed from the vortohrm, and join the sternum or breast bone, 
are called true ribs ; tliose which do not extend so far are termed false ribs. In Quad- 
rupeds tlu-^e false ribs are always behind ; in Birds they are both before and behind. 
This distiiietion ceases to prevail in animals that have no sternum. The sternum is 
absent in Servients and Fishes, unless we give that name to denote the anterior part of 
tlie bony girdle, which supports the pectoral fins, or anterior extremities of the 
Fishes. Several Fi.shcs have no very apparent nock. 
TIic Vertebrata never have more than two pair of limbs; but these 
are somciimes altogether wanting, or only one pair of them is deficient. 
The forms of their limbs vary according to the movements wiiich they 
arc destined to execute. The fore or anterior limbs may be so organized 
as to pcrruriii the office of hands, of feet, of wings, or of fins; the hinder 
may be cither feet or fins. 
The limbs arc totally wanting in Serpents and in some Fishes. The fore limbs arc 
absent m one species of Lizard; while the hinder limbs arc not found in tho Apodes 
order of that is to aav, in those having no vential fins; and also in the Ceta- 
ceous tribes of Mammalia. No Vertebrated animal ever has more Inan four limbs, 
unless wc includ:; in the number the kind of wing which belongs to the Flying Dragon 
(Draco volaaSf Linn.J, a little animal next to our Lizard. 
The Limbs, when perfect, arc divided into four parts. Tim fore limbs comprbe 
the Shoulder, the Arm, the Fore Arm, and the Hand; tho hinder limbs contain the 
Hip, Thigh, Leg, and Foot. These distinctions do not hold among those Fishes 
having their limbs consisting only of bony rays; tliat is to say, of bones constituted 
like a fan, and articulated to parts corresponding with the shoulder or hip : yet even 
some analogy may be found belwceu these parts and the divisions in tho limbs of the 
higher animals. 
The shoulder consists of tlie Scapula, placed against the back, and the Clavicle 
attached to the Sternum. The last is wanting in aomo Quadrupeds, as well as in the 
Cetacea, as wiU be explained hereafter; but it is double in Birds, Tortoises, Frogs, 
and many Lizards. The Scapula is never wanting when the fore limb exists. The 
Arm is formed of one bone only ; and the fore arm Ls almost always formed of two. 
Even when the fore arm has but one bone, there generally appears a furrow, or other 
vestige, of its ordinary construction. The Hand v*aries with rc<q)cefc to the number 
of its bones; but those which exist in it always form the Wrist or Carpus, the body of 
tho hand or Metacarpus, and the Fingers. Tbia organization prevails even in Birds, 
which have their fingers enveloped in a skin covered with feathers. It likewise prevails 
in the Cetacea, in which the whole of the fore limb is reduced to the figure of an oar 
or fin. 
The parts of the skeleton are usually disposed with a strict regard to symmetry; so 
that the halves of tho body formed by a longitudinal section are exact counterparts 
of each other. In one family of Fishes only, called Pleuronectes, including Soles, 
Plaice, Turbots, and other Hat Fishes, the head is so formed that tho two eyes and 
two nostrils are on the same side, but the symmetry is preserved in the remainder of 
the skeleton. 
Each class and each order of animals have particular characters relative to their 
skeleton; consisting in the general form of their trunks and limbs, and in the number 
of their different parts. These particulars will bo explained in tho future jiages of 
the Animal Kingdom. Wc may, however, remark here, that though an animal of one 
class may have some resemblance to those of another, in the form of its parts, and the 
use it makes of them, that resemblance is oxlernal, and affects the skeleton only in its 
proportions, but neither in the number nor in the arrangement of tho boues. Tlie Bats, 
for example, appear to have wings; but an attentive examination demonstrates that they 
are real h-inds, the fingers of which arc merely somewhat lengthened. In tho same 
manner, though the Dolphins appear to have fins all of one piece, wc find under the 
skin all the bones that compose the fore limbs of the other Mammalia, only shortened 
and rendered almost immoveable. The nings of the Penguin, which likewise resemble 
fins in ono piece, contain internally the same bones as those of other Birds. 
Tho skeletons of the Veriebrated animals determine their most important forms 
and proportions. Retaining a general resemblance throughout all the classes of this 
division, they do not tlifler so much as thoir oxlernal figures, while they preserve a 
remarkable uniformity, which would not be always anticipated from tho aspect of the 
ports they sustain. This property cannot be observed among the Invcrtebratcd 
animals, because their hard parts are placed externally, and must therefore have the 
same forms as the animals themselves. 
In general tho bones are joinoil or articulated together, thus forming one connected 
frame; but some exceptions to this law arc to be found. The bones supporting the 
tongue in Mammalia and Birds are not connected with the other bones except by soft 
parts, though in Fishes they are articulated to the rest of the skeleton. Again, the 
entire of the fore extremities in quadrupeds destitute of clavicles arc attached to the 
remainder of the skeleton by muscles only ; but in the others they arc united to tho ster- 
num by single clavicles, or collar bones. Among Birds this union is effected by double 
clavicles. In the Fishes, a bony girdle connects the bones of the fore fins strongly 
with the spine. The skeletons of the hinder fins of the Fishes, on the contrary, arc 
usually isolated, aud fixed only in the muscles; while, in the other three classes, the 
hinder extremities arc always attached strongly to tlio rest of tho skeleton by means 
of the pelvis, or arc wanting altogether. 
It has already been explained that the bones of the Vertebrata are composed prin- 
cipally of phosphate of lime and of animal matters, such as gelatine, cartilage, ami 
marrow. The quantity of the calcareous phosphate increases in tho bones with age; 
the gelatinous substance, on tho contrary, appears most abundant in proportion as it 
is examined near to the period of birth. The bones of the fmtus, ia tho earlier period 
of existence, consist merely of cartilage or indurated jelly; for cartilages resolve almost 
entirely into jelly when subjected to tho action of boiling water. In the very young 
embr} 0 there is no real cartilage ; in its place wo observe a substance which has all 
the appearance, and oven the scmi-fiuidity, of ordinary jelly. It has already assumed 
a determinate shape, and is covered by a membrane, which afterwards forms tho exter- 
nal covering of the bones, or periosteum. The fiat bones, again, have tlie appoaraueo 
of simple membranes during the first stages of ossification. Those which are intended 
to move on each other exhibit visible articulations, although the periosteum passes 
from one to the otlicr, aud onvclopes the whole in ono common sheath ; while thoso 
connected only by sutures, such as the bones of the skull, form a continued whole, 
in which nothing indicates that these sutures will one day exist. 
The phosphate of lime, wliich gives consistency and strength to the bones, ** 
deposited in this gelatinous basis; this deposition does not proceed irregularly, but 
by laws, fixed and determinate fur eacli bone. During ossification, wc first observe 
fibres developing themselves separately; and these are shortly succeeded by new and 
smaller fibres, extending in every direction, and uniting the former into one uniform 
mass. 
The surfaces of bones arc generally formed of close and compact fibres, which are 
placed parallel to each other in the long bones, but diverge like radii, from centres la 
the flat bones. These fibres proceed from certain systems of points called centres of 
ossification. Each long bone has usually three systems of this kind; one towards HS 
middle, where a series of ossifying points surround it like a ring, having the bony 
fibres extended in a direction parallel to the axis; and another principal centre at cac 
extremity of the bone, sometimes accompanied with several subordinate points. Wh'nj 
the three bony pieces, formed by the successive extension of these three centres o 
ossification, have even approached so os to be in contact w ith each other, they rcmaia 
