M A M M A L I A. 



Ill 



the circular liead of a bone is introduced into a cavity 

 of a similar form. The most perfect ones of this kind 

 are the articulations of the thigh bone with the hip 

 bone, and that of the arm bone with the blade-bone, 

 and there are less perfect instances in the thumbs. 

 Very often, however, a motion of this kind is obtained 

 by the intervention of a number of bones, \vhich all 

 i-ontribute to the motion to some extent or other, 

 though it is not very easy to assign each its proper 

 share : the curious motions of the wrist, which may be 

 Raid to be in all imaginable directions to which the 

 members can be bent, are perhaps the most remark- 

 able instance of this, not only in the human subject, 

 but among the whole mammalia. 



In those joints which have the most general mo- 

 tion, arising from the peculiar motion of two bones, 

 there are two precautions against the chance of dislo- 

 cation. The hip joint, which, though it is a ball and 

 socket, still has its most powerful motion in the mesial 

 plane, has the ball united to the middle of the socket 

 by a round ligament, which partly forms a pad be- 

 tween tho acting surfaces, and partly allows a more 

 free motion, but prevents the bone from slipping out 

 of its socket. Other joints, such as the joint of the 

 knee, which have their principal motion hinge-ways 

 by means of two condyles and two cavities, have a 

 division between thecondyles in which there are liga- 

 ments placed crossing each other, and allowing, at 

 the same time, free motion to the joint. Such joints 

 are generally also inclosed in ligamentous matter, 

 which forms a border round the brim of the cavity, 

 and extends over the condyle and part of the bom-. 

 These ligaments are, like the others, elastic, and when 

 the joint is strongly bent in one direction, there is a 

 tendency in the ligament to bring it back again, if 

 the muscular action is suspended. 



The position of repose, or perfectly easy rest, in 

 animals which stretch themselves down to rest, as- 

 sumes that of a uniform balance of the ligaments, at 

 least in the limbs of the animal. The muscles are 

 the portions of the animal structure which are soonest 

 tired by exertion, and the position of rest at perfect 

 ease is that in which all the muscles are equally in a 

 state of repose ; and any one may know whether a 

 limb is in a state of complete repose or not by trying 

 whether external force will bend it with equally little 

 exertion in all the directions in which it naturally 

 bends. Painters and others, who endeavour to re- 

 present the positions of animals and their parts, whe- 

 ther in a state of action or in a state of repose, often 

 commit sad blunders from ignorance of the mecha- 

 nical action of the animals. They often lay a figure 

 down in repose, or even asleep, with all its limbs in 

 a state of great muscular excitement ; and they as 

 often represent a limb as in the act of performing 

 scum.- mighty deed, when the said limb is in a state 

 of perfect inaction. The most ludicrous blunder of 

 this kind is that in which violent action is endeavoured 

 to be represented ; for, in these cases, an assassin may 

 be represented as in the ver}' act of felling his victim 

 to the ground with a bludgeon, or of stabbing him'to the 

 heart with a dagger, and yet the muscles which extend 

 the arm and those which draw it back may be both 

 so equally excited in the representation that the arm 

 could not possibly move a hairbreadth. We must, 

 hi'wever, close our observations on the bones and 

 their adaptation for motion, for to exhaust the subject, 

 even on the human body alone, would be a vain ex- 

 pectation. What is already known would fill many 



volumes, and the unknown would, in all probability, 

 fill a far greater number. 



The MUSCLES. As the muscles, or immediate or- 

 gans of motion, vary in their forms according to the 

 state of action or repose that they are in, and as from 

 their being wholly composed of soft animal matter 

 they are subject to perish, or at all events to lose 

 their original shape far sooner than the bones, we 

 shall not go into even a list of them, but content our- 

 selves with a few remarks on their nature and mode 

 of action, and on those appendages which connect 

 them with the parts which they move, or keep them 

 in that shape in which they can perform their offices 

 most effectively, and with the least exertion on the 

 part of the animal. 



Wherever a muscle appears, or to which ever of 

 the functions of the animal it ministers, its general 

 structure and general mode of action are the same, 

 though from the number of different motions of which 

 they are the organs, their shapes, sizes, and relative 

 degrees of strength vary much. 



Various divisions of the muscles into classes have 

 been proposed, according to their supposed con- 

 nexion with what is called the will of the animal, and 

 also according to the fancied system in the animal of 

 which they are supposed to form a part. Such dis- 

 tinctions are, however of little or no value. The 

 question of will is one which should be introduced as 

 seldom as possible, for this very plain reason, that 

 nobody can tell what it means; and, instead of the 

 muscles of the arm being voluntary or obedient to 

 the will, and the muscles of the heart involuntary, or 

 not obedient to it, the whole difference is, that the' 

 external one, exposed as it is, and temporary as it is 

 in its use, is not so easily or so constantly excited to 

 action as the internal muscle, which is defended from 

 the air, preserved uniformly at a high temperature, 

 and has the stimulus of the blood always applied to 

 it in the course of the circulation. The real ground of 

 distinction is, therefore, one concerning the causes 

 which stimulate muscles ; and as the actions which 

 the different mammalia, to leave all other animals 

 out of the question, have to perform in nature are 

 perfectly innumerable, and as we know nothing about 

 the stimulus or cause of action in the muscle farther 

 than as we see of the animal which possesses it, and 

 the circumstances which appear to us to stimulate the 

 animal to action, we cannot draw the line of distinc- 

 tion between what is voluntary and what is not. So 

 much, indeed, is this the fact, that even in our own 

 case, where we may naturally be supposed to have 

 the best information, we cannot confidently say that 

 we are possessed of any thing called w'ill, which 

 comes in as a sort of third party between us and the 

 circumstances under which we act in any given man- 

 ner. At all events, will can never be of any practical 

 use, unless it advances as far at least as can, and 

 therefore it is not a fit subject for popular writing, 

 and perhaps not for instructive writing of any kind. 



The best way, therefore, is to disregard all those 

 metaphysical or systematic distinctions, and deal with 

 the muscles just as we do with the bones that is, de- 

 scribe them according to their forms and situations in 

 the body, and the functions which we see them per- 

 form, without ever troubling ourselves why a muscle 

 produces motion and a bone does not, or why one 

 muscle appears to perform one kind of motion and 

 another not. In all the varied motions and actions 

 of the animal body, the muscle, considered as sub- 



