104 



3VI A M M A LI A. 



but the working ends are covered with cartilage of a 

 bluish-white colour, and very elastic ; this differs in 

 its chemical nature from the basis of the rest of the 

 bone, for it contains a good deal of albumen ; and it 

 is worthy of remark, that there should be this differ- 

 ence between the mere cement which retains the 

 earthy matter, whereby strength is given to the bone, 

 and that which enables the extremity of one bone to 

 work smoothly on another. There is an oil provided 

 by nature for all those working extremities, but they 

 are themselves also very smooth, and composed of 

 matter which is very elastic, so that they are but 

 little liable to jolt, which, in the more violent motions 

 of animals, would shatter the bones to pieces. No 

 doubt the! way in. which the different bones come 

 into action contributes a great deal to this purpose, 

 for it never strains directly upon the end of a bone, 

 nor yet on the side of it, so that one bone supports 

 another. By this means, a blow given with the extre- 

 mity of the limb is capable of breaking a substance 

 stronger than any part of the limb itself. 



The cartilaginous basis of the bone is an elastic or 

 flexible substance, as well as that which covers the 

 moving parts ; and it does not appear that any truly 

 animal formation, while it is in the living state, can 

 acquire such hardness as to be stiff and indexible. It 

 is reasonable to suppose that this should be the case, 

 because living matter is in a state of continual change, 

 by the old being taken up and new deposited in its 

 place, and it does not appear how this could be done 

 in an inflexible solid. Hence the bones are rendered 

 stiff by the accumulation of a quantity of earthy mat- 

 ter in the cells or interstices of the cartilaginous bases. 

 Those earthy matters are all salts of lime, the same 

 as they exist in minerals, or any where else, without 

 any reference to their being products of animal life ; 

 and therefore, though they are unquestionably depo- 

 sited in the bones by the action of the animal, they 

 cannot in themselves be regarded as animal matter 

 that is, matter which it would be vain to seek for any 

 where save in the structure of an animal. They con- 

 sist chiefly of phosphate of lime, carbonate of lime, 

 and sulphate of lime, of which the first predominates 

 in all bones except the enamel of the teeth. It is 

 less dense than the other salts of lime, and not so brittle. 



How these salts of lime come to be deposited, we 

 can no more tell than we can tell why any animal is 

 of one specific form and not of another. We are 

 certain, however, that it does not exist in the very 

 earl^stages of lite, because there is no earthy matter 

 in the bones then ; and, though we know not the pro- 

 cess, we can observe the progress of its formation. 

 The process is called ossification, which means chang- 

 ing to bone ; and it appears to be an operation of the 

 bone itself, for it always takes place in the middle, 

 and proceeds gradually from a series of points, until the 

 whole bone is ossified. It appears, also, that this com- 

 plete ossification limits the growth of the bone, and that 

 before it is absolutely completed the stature of the 

 animal ceases to increase. It appears, also, to be the 

 part of the animal system which, in the gradual decay 

 of nature, and without any local injury or casualty of 

 disease, is the first to give way. We seldom see 

 wild animals in a state of decrepitude ; because, de- 

 pending wholly on their animal resources, they are 

 more liable to contingencies than human beings ; but 

 we readily perceive, in the decay of the human sub- 

 ject, a remarkable exhaustion of the bones before the 

 structures which are more immediately concerned in 



the functions of life begin to give way. Their limbs 

 become feeble and tottering, their vertebral columns 

 bent; and they seem gradually to sink towards that 

 grave which is the place of final repose for every ani- 

 mal body. In these cases it is evident that some 

 contraction takes place in the bones ; they are dried 

 of their juices, and there is reason to believe that 

 either their salts of lime are taken up by the absorb- 

 ents, or the materials necessary for their formation are 

 retained in the larger vessels, and precipitated on 

 their coats, forming what are usually termed ossified 

 vessels. 



Besides the cartilaginous base and the salts of lime, 

 which give stiffness, every bone is covered externally 

 by a firm membrane, the periosteum, which means 

 that which is round the bones. This membrane does 

 not extend to the working surfaces of the bones, or . 

 those which are covered with cartilage ; it reaches 

 nearly as far as the parts which are actually bone. It 

 is exceedingly sensitive ; and it becomes indurated 

 in its substance as the animal waxes older. In the 

 young animal, its connexion with the bone is but 

 loose, but as the animal advances in age it adheres 

 more and more firmly. It appears to be essential 

 to the healthy state of bone, for if the periosteum is de- 

 stroyed from any part, the surface of the bone scales 

 off or exfoliates ; and if the periosteum becomes dis- 

 eased, it speedily eats into the substance of the bone, 

 and destroys its texture. Such are the leading par- 

 ticulars of the supporting structure of the mammalia, 

 in so far as the substance, growth, and decay of that 

 structure are concerned ; and we shall now advert to 

 the arrangement of the bones in the human skeleton, 

 to which we can afterwards refer as a standard, in 

 order to show how the divarications from this stand- 

 ard, which we find in the other animals, are essential 

 to their more confined and localised species of action. 

 In the human skeleton skeleton is the name of the 

 entire bony structure of an animal, and is peculiar to 

 vertebrated animals, in the human skeleton, as in 

 all the others, the vertebral column, or spine, is the 

 foundation upon which the whole skeleton is organ- 

 ised ; and, indeed, as vertebrated animals are the only 

 ones in which the system of sensation, the charac- 

 teristic animal system, is fully developed, it may be 

 said that the whole structure of the animal is founded 

 upon this column and its contents. One extremity 

 of this column supports the head, and the other extre- 

 mity is supported by the feet, through the medium 

 of the bones of the pelvis or lower cavity. The 

 bones themselves are so many, that it is necessary to 

 classify them so as to remember the groups, and then 

 each group becomes a sort of index to the individual 

 bones of which it is composed. 



The first and most obvious division is into the 

 head, the trunk, and the extremities; and this division 

 applies to the whole class of mammalia. The bones 

 of the head admit of subdivision into those of the 

 cranium and those of the face ; the former enclosing 

 and defending the brain, which is understood to be 

 the most important organ of a sentient animal ; and 

 the bones of the face supporting the mouth and those 

 organs of sense which are directed to the front. The 

 cranium consists of eight bones, and the face of fifteen, 

 besides the thirty-two teeth, which do not come pro- 

 perly within the class of ordinary bones. 



If we include these in the number, and also the 

 peculiar bone of the tongue, and the small bones in the 

 apparatus of the ear, the total number is sixty-three. 



