AKIMALIA VERTEBRATA— VERTEBRATED ANIMALS. 
21 
described with the sraiiG radius, shall exactly fit and correspond at their extremities. 
In each, the mind is led from one link to another by insensible shades, almost with- 
out perceiving any interval. 
On considering each organ separately, and following it through all the species of 
one class, wo observe that its progression, within certain limits, is preserved with a 
singular regularity. The organ, or some vestige of it, is to be found even in species 
^here it is no longer of any apparent use. except to prove that Nature strictly adheres to 
the law of doing nothing by sudden transitions. Yet, the organs do not all follow ths 
same order of gradation. One part is found absolutely perfect in a certain animal, 
while another part is in its most simple form. Again, on examining a different animal, 
the relative complication of the two organs is absolutely reversed. If, therefore, w*o 
wore to class different species according to each organ taken separately, we should bo 
undor thc necessity of forming as many series as wo should have regulating organs. 
Tims, to make a general scale of complication, it would be essential to calculate 
the precise effect resulting from each combination, which is far from being practi- 
cable. 
As long as the groat central springs remain the same, and v/hile we confine our- 
selves to the same combinations of the principal organs, these gentle shades of an 
insensible gradation are found to prevail. All the animals of each of the primary 
divisions seem formed on a common plan, which serves as the basis of all their minute 
external modifications. But the moment that \vc direct our attention from one prin- 
cipal group to another, wherein different leading combinations take place, the scede 
directly changes. Thure is no longer any resemblance, and an interval, or marked 
transition, is obvious to every one. Thus, it is impossible to find in the whole Animal 
Kingdom any two being!* which sufficiently resemble each other to serve as a link 
between the Vertebrated and Invcrtebrated animals. 
The Creator, never outsteps the bounds which he has proscribed to himself in the 
laws of tlic conditions of existence. Bver adhering to the small number of combina- 
tions tliat are possible, Nature seems to delight in varying the arrangement and struc- 
ture of the accessory parts. There appears in them no necessity fora particular foiun 
or arrangement, while it frequently happens, that particular forms and dispositions are 
created without any apparent views of utility. It seems only .sufficient for their exist- 
ence that they should bo possible, that is to say, that they do not disturb or destroy 
the harmony of the whole. These varieties augment in number, in proportion as we 
turn our attention from the leading and essential organs to those which are less 
important; and when wc finally arrive at the external surface of the body, where the 
laws of external Nature require that the least essential oi^ans, and those least liable 
to injury, should be placed, we find the number of varieties absolutely infinite. The 
labours of naturalists have not yet succeeded in tracing all their differences, and newly- 
discovered species are continually rising, as it were, into existence. Yet not even is 
a bone varied in its surfaces, in its curvatures, or in its eminences, without subjecting 
the other bones to corresponding variations. 
THE FIRST GREAT DIVISION OF THE ANIMAL KINGDOM. 
ANIMALIA VERTEBRATA— VERTEBRATED ANIMALS. 
IIAVIN-G A nONY SKELETON, CONSISTING OF A CK.ANIDM, SFINAL COLUMN, AND GENERALLY ALSO OF LIMBS; THE MUSCLES ATTACHED TO THE SKELETON, 
DISTINCT ORGANS OF SIGHT, HEARING, SMELL, A.ND TASTE, IN THE C.AVITIES OF THE FACE; NEVER MORE THAN FOUR LIMBS; SEXES SEPVRVTE; BLOOD 
ALWAYS IlED. 
The bodies and limbs of the Vertebrated Animals are sustained by a solid 
framework or skeleton, composed of separate pieces joined together, 
Hnd moveable upon each other. This enables them to execute their 
luoveinents wuth vigour and precision ; while the solid suj)port afforded 
hy the hones permits them to attain a considerable size. It is, conse- 
quently, in this division that the largest animals are found. 
There are three important purposes answered by the bones of Vertebrated Animals: 
a solid framework is supplied to tlic softer parts ; bases arc furnished upon which the 
ttuiscles are fixed; and u protc.etion from external injury is afforded to the vital parts, 
and to the central masses of the nervous system. 
A limit to the size of animals is fixed by the force of gravity at the earth’s surface. 
V orc animals to exceed this limit, they would fall to pieces by the weight of their 
limbs; and a certain degree of cohesion, constituting rigidity, is inconsistent with ani- 
mal motion. This forms a complete refutation of the idle tales of crakens, giants, 
*nd other monsters. 
The nervous system of the Vertebrata is more concentrated, and its 
central masses arc of greater size than in other animals. Their sensa- 
tions also are more vivid and prolonged, and they possess superior intel- 
ligence and capacity for improvement. 
T'he bodies of the Vertebrata are always composed of a head, a trunk, 
and [generally] also of limbs. 
The head is formed of the cranium or skull, and of the face. The 
former contains the brain, and in the latter are placed the receptacles 
for the organs of sense. 
The liumon skull is composed of eight bones, one frontal, two parietal, one occipi- 
two temporal, one sphenoid, anil one fcthmoid. The fronb'-l bone (or os froiiiis), 
lorms the entire covering of the forehead, vrilh the upper orbit of the socket for the eye, 
and extends towards the temples. In the infant, this bone was originally two, which 
'ave gradually coalesced into one. Two parietal banes (vssa p^uittalla) form the 
^^des and upper part of the skull. The occiput, or hinder bone of the head (os occi~ 
forma the base of the skull. There are two temporal lioncs (ossa iewpo^ 
one on each side; and one sphenoid bone (sphcnoidcs.^ The prinripal part 
tbe sphenoid bone, and tho whole of the oithmoid (athmoidcs), are placed in tho 
^teriiiil part of tho skull ; they support tho brain, and allow the nerves to pass through 
neir irregular gi’oovcs and cavities. 
hqtho skull of the fatus, during the earlier months of its existence, cartilage is 
*‘uhsUtutod for bone. Ily degrees porlions of the cartilage are absorbed, and earthy 
imu'los are as gratluaViy deposited in their places from certain points, which arc 
called centres of ossification- 
form, which was rudely defined at first, advances by gradual steps toward 
definite and fixed laws. A certain system of ossifying centres bc- 
hav 
to each separate bone. The fibres proceeding from centres of the same hone, 
^ ^ natural affinity for each other, and generally refuse to unite with the fibres of 
^ cr bones. Tliis, however, sometimes takes place, as in the Os fronilSf when tho 
^ said to Turin an anchyhsis. 
s these hones of the skull are destined to protect the brain, they are formed in a 
^^anner peculiarly atbipted fur that purpose. Each bone is composed of two plates; 
mtcrnal layer (or iabida vitrea) is dense, hard, and well adapted to resist a vio- 
blow; the external layer is fibrous and lough, and fitted to check the vibration 
6 
of the internal part. It has been rightly compared to a soldier’s helmet, lined with 
Icatlier and ornamented with Imir, 
The edges of the bones, where they meet together, ai*c beautifully dovc-tailed, 
forming sutures, which give the wlnde skull vmity and strength. Those irregular 
lines of junction arc formed hy the fibres of opposite centres, which continue to secrete 
tlic bony particles, and to insinuate themselves until finally stopped by their mutually 
inercased resbtance. 
Fourteen bones compose tho human face. These are usually grouped together 
under the names of upper and lower jaw’s. They consist of two superior maxillary, 
two malar, two nasal, two palate, two lachrj'mul, two turbinated, one vomer, and one 
inferior maxillary bone. Of these, the most remai-kablo is the lachrymal, which con- 
sists of a delicate bony scale, as thin as paper, and containing tho passage which 
conveys tho tears from the eye into the nasal cavity. 
The relative size and arrangement of the bones of the face and skull vai-y consider- 
ably in different tribes of animals. 
Tho head is always placed at the anterior extremity of the vertebral column, and 
opposite to the tail. It is divided into three parts, which may vary in their relative 
proportions, but are never wanting. 'J'hese divisions arc, first, the Cranium, contain- 
ing the brain, in the pai-fcitions of which are situate the cavities of tho internal car, 
and frequently a part of those of the nose; secondly, the Face, terminated below by 
the upper jaw, and containing the orbits of the eyes, with the nasal cavities; and 
thirdly, the lower jaw. 
Tlic trunk is sustained by tlic spine of tlie back and by the ribs. 
The spine is composed of vcrtebriE. Each vertebra is, in genera], 
moveable on the adjoining ones. The first carries the head; and through 
each vertebra there is an annular or nng-like part, all of whicli collectively 
form a canal. In this canal is placed that portion of tlie medullary sub- 
stance called the spinal marrow, from whicli tlie nerves proceed. 
In the spinal column of adult animals, great strength is. combined with a consider- 
able degree of general flcucure. The aiTangcincnt of the'solid matter of which it is 
composed, is admirably calculated to give lightness to the whole fabric. It is neither 
collected into one solid mass, nor generally diffused as in sponge. But the column is 
hollow; and, by the laws of IMcchantcs, it has been clcaidy ascertained that while tho 
height and the quaiiiily of matter of two pillars remain the .same, that column is the 
stronger which is, to a certain degree, of a hollow construction. 
The cartilages between the several vertehrm yield considerably lb the pressure of 
the body, after remaining for a long time in tho vertical position, and expand after 
repose. Hence arises tho very striking phenomonon, that a man is considerably taller 
in the morning after a nights rest, than in the evening after the fatigues of the day. 
Tho long absence of pressure upon the o.Tjtilages of the verlobra; causes them to 
expand, fins difference of height has boon observed only in the. human spccios; they 
arc the only crcaturijs who walk erect, and throw the pressure of the upper pai ts uf 
tho body upon the back hone. 'I'hus we find no ilifforcncc in the height of horses, 
even after the longest day’s journey. 
Among young people this differeneo is more observable than in those who are more 
aged. Persona of very laborious habits sink rather less than those of sedentary habits ; 
and when the height is mice lost, it ciumot be restored for that day, not even by tho 
use of the cold bath; and it can be alone regained by a night’s repose in a horizontal 
position.* 
* Philosopliical Transactions, No. 383, p. 87. 
