22 



THE FIRST GREAT DIVISION. 



The Reverend Mr. Wasse fuund that several persons, enlisted as soldiers in the 

 morning, had 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 not less than an inch. 

 This gentleman observed, from his ovfn personal experience, that on fixing a bar of 

 iron, which he just readied 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 the laborious kind. He 

 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 whole inch of tiis height. 



It appears evident that this change is occasioned merely by the back boncj from 

 the circumstance that 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 than 

 in Man. By the thickness and shortness of the several vertebra;, and by the inter- 

 vening cartilages, with the bony projections, it is adapted for motions peculiar to itself. 

 Had the several vertebrae 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 were 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 cartilages of the 

 three kinds of vertebrae are other singular instances of exquisite arrangement. 



The vertebree of the back require but little motion; and the cartilages in that part 

 of the column are 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 

 greater weight. It therefore follows, that during the period of the day in which we 

 are actively engaged in the several duties of life, until we 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, wlien this superior weight is entirely removed, by placing 

 the body in the Viorizontal position, as it always is when we are in bed, the compi'essed 

 cartilages will begin to enlarge themselves, until they gradually recover their expanded 

 state. 



As the cartilages between the several vertebrae are twenty-four in numloer, 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 the 

 weight of the body alone upon the spinal column; it must therefore be much greater in 

 persons constantly employed in carrying burdens. That the compression and expansion 

 of the cartilages in older people is less than in younger, is a necessary consequence 

 of the cartilages growing harder in the course of time, and becoming less capable of 

 compression. It also follows, that old persons must lose some pai-t of their former 

 height, from the cartilages shrinking into a smaller compass as they grow bony ; and 

 this shortening, or "growing downwards," is not imaginary, as persons commonly 

 suppose, but a real phenomenon. 



In general, the spine is prolonged into a tail, extending beyond the lower 

 extremities. 



'Man possesses a kind of rudimental tail, in the os coccygist terminating the spinal 

 column. Among Mammalia, the Ternate Bats alone are destitute of this rudimental 

 tail; it is wanting altogether in the Batrachia or Frog tribe. 



The ribs may be compared to semi-circular hoops, which protect the 

 sides of the cavity of the trunk. They are articulated at one extremity 

 to the vertebras, 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 are scarcely visible. 



The vertebrae are never entirely wanting, although their number is exceedingly 

 variable. Those which sustain the ribs are called dorsal; those between the dorsal 

 and the head are termed cervical ; those below the dorsal, lumbar ; those connected 

 with the pelvis, or hinder extremity, sacral or pelvic ; and those forming the tail, 

 coccygeal or caudal. The ribs ai*e wanting in Frogs, also in Rays, Sharks, and a 

 great number of cartilaginous Fishes. It is obvious that in the animals without ribs, 

 the distinction of the three first kinds of vertebra; cannot take place, and that the 

 distinction of the three last disappears in those having no hinder limbs, or where their 

 limbs are not attached to the spine. 



The ribs which proceed from the vertebrae, and join the sternum or breast bone, 

 are called true ribs; those which do not extend so far are termed false ribs. In Quad- 

 rupeds these false ribs are always behind; in Birds they are both before and behind. 

 This distinction ceases to prevail in animals that have no sternum. The sternum is 

 absent in Serpents and Fishes, unless we give that name to denote the anterior part of 

 the bony girdle, which supports the pectoral fins, or anterior extremities of the 

 Fishes. Several Fishes have no very apparent neck. 



The Vertebrata never have more than two pair of limbs ; but these 

 are sometimes altogether wanting, or only one pair of them is delicient. 

 The forms of their limbs vary according to the movements which they 

 are destined to execute. The fore or anterior limbs may be so organized 

 as to perform the office of hands, of feet, of wings, or of fins ; the hinder 

 may be either feet or fins. 



The limbs are totally wanting in Serpents and in some Fishes. The fore limbs are 

 absent in one species of Lizard; while the hinder limbs are not found in the Apodes 

 order of Fishes, that is to say, in those having no ventral fins; and also in the Ceta- 

 ceous tribes of Mammalia. No Vertebrated animal ever has more than four limbs, 

 unless wo include in the number the kind of wing which belongs to the Flying Dragon 

 (Draco oolans, Linn.), a little animal next to our Lizard. 



The Limbs, when perfect, are divided' into four parts. The fore limbs comprlsa 

 the Shoulder, the Arm, the Fore Arm, and the Hand; the hinder lirnbs contain the 

 Hip, Thigh, Leg, and Foot. These distinctions do not hold among those Fishes 

 having their limbs consisting only of bony rays; that is to say, of bones constituted 

 like a fan, and ariiculated to parts corresponding with the shoulder or hip : yet even 

 some analogy may be found between these parts and the divisions in the limbs of the 

 higher animals. 



The shoulder consists of the Scapula, placed against the back, and the Clavicle 

 attached to the Sternum. The last is wanting in 3ome Quadrupeds, as well as in the 

 Cctacea, as will 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 is 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 varies with respect to the number 

 of its bones; but those which exist in it always form the Wrist or Carpus, the body of 

 the hand or Bletacarpus, and the Fingers. This 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 hmb is reduced to the figure of an oar 

 or fin. 



The parts of the skeleton are usually disposed with a strict regard to symmetry; eo 

 that the halves of the 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 Flat Fishes, the head is so formed that the two eyes and 

 two nostril? 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 be explained in the future pages of 

 the Animal Kingdom. We may, however, remark here, that though an animal of one 

 class may have some resemblantie to those of another, in the form of its parts, and the 

 use it makes of them, that resemblance is external, and aifccts the skeleton only in its 

 proportions, but neither in the number nor in the ai*rangement of the bones. The Bats, 

 for example, appear to have wings ; but an attentive examination demonstrates that they 

 are real hands, the fingers of which are merely somewhat lengthened. In the same 

 manner, though the Dolphins appear to have fins all of one piece, we find under the 

 skin all the bones that compose the fore limbs of the other Mammalia, only shortened 

 sind rendered almost immoveable. The wings of the Penguin, which likewise resemble 

 fins in one piece, contain internally the same bones as those of other Birds. 



The skeletons of the Vertebrated animals determine theii* most important forms 

 and proportions. Retaining a general resemblance throughout all the classes of this 

 division, they do not differ so much as their external figures, while they preserve a 

 remarkable uniformity, which would not be always anticipated from the aspect of the 

 parts they sustain. This property cannot be observed among the Invertebrated 

 animals, because their hard pai-ts are placed externally, and must therefore have tha 

 same forms as the animals themselves. 



In general the bones are joined or articulated together, thus forming one connected 

 frame; but some exceptions to this law ai"c to be found. The bones supporting the 

 tongue in Mammalia and Birds are not connected with the other bones except by soft 

 pai'ts, 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 are united to the ster- 

 num by single clavicles, or collar bones. Among Birds this union is efi'ected 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, and fixed only in the muscles; while, in the other three classes, the 

 hinder extremities arc always attached strongly to the rest of the skeleton by means 

 of the pelvis, or ai'e 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, cai'tilage, and 

 marrov/. The quantity of the calcareous phosphate increases in the bones with age ; 

 the gelatinous substance, on the contrary, appears most abundant in proportion as it 

 is examined near to the period of birth. The bones of tho foetus, in the earlier period 

 of existence, consist merely of cartilage or indurated jelly; for cartilages resolve almost 

 entirely into jelly when subjected to the action of boiUng water. In the very young 

 embryo there is no real cartilage ; in its place we observe a substance which has all 

 the appearance, and even the semi-fluidity, of ordinary jelly. It has already assumed 

 a determinate shape, and is covered by a membrane, which afterwards forms the exter- 

 nal covering of the bones, or periosteum. The flat bones, again, have the appeai-ance 

 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 other, and envelopes the whole in one common sheath ; while those 

 connected only by sutures, such as the bones of the skull, form a continued whole, 

 in which nothing indicates that these sutm-es will one day exist. 



The phosphate of hme, which gives consistency and strength to the bones, is 

 deposited in this gelatinous basis; this deposition does not proceed irregularly, but 

 by laws, fixed and determinate for each bone. During ossification, we 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 are generally formed of close and compact fibre*;, which are 

 placed parallel to each other in the long bones, but diverge like radii, from centres in 

 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 its 

 middle, where a series of ossifying points surromid it like a ring, having the bony 

 fibres extended in a direction parallel to the axis ; and another principal centre at each 

 extremity of the bone, sometimes accompanied with several subordinate points. When 

 the three bony pieces, formed by the successive extension of these three centres of 

 ossification, have even approach.ed so as to be in contact with each other, they vemaia 



