112 



M A M M A L I A. 



stantive matter, can perform no action and originate 

 no motion, unless we trace it downward as connected 

 with the race from its original creation as a living 

 creature, how often so ever it may have passed through 

 the embryo state during the interval. All our in- 

 quiries respecting the action of muscles must, there- 

 fore, be confined to what they do, and the manner in 

 \vhich they do it, because, as to why they do it, we 

 can get no information. 



Muscles consist almost entirely of fleshy fibres, 

 generally arranged parallel and formed into bundles, 

 which bundles, as well as the more minute fibres of 

 which they are composed, are all encased with cellu- 

 lar tissue. This tissue admits a ready passage to the 

 numerous blood-vessels, nerves, and lymphatic ves- 

 sels, with which muscles, in the mammalia at least, 

 are always copiously provided. The bundles of fibres 

 of which a muscle is composed, are variously disposed 

 in the muscle. When they run longitudinally through 

 the whole of it parallel to each other, it is called a 

 straight muscle ; but it is sometimes run obliquely 

 across the general substance of the organ, sometimes 

 they diverge from partitions dividing the muscle in- 

 ternally, and sometimes they are disposed in a circu- 

 lar manner. The last mentioned structure occurs in 

 the iris of the eye, which, in diurnal mammalia, con- 

 tracts to a point by the action of light ; but the eyes 

 of climbing animals, which are nocturnal, generally 

 speaking contract to a vertical line, while those which 

 range the surface of the ground often have the iris 

 contracting in a horizontal line. 



In all muscles which give motion to the limbs and 

 other articulated parts of animals, it is the distal bone, 

 or bone most remote from the body of the animal, or 

 from the spinal column in the mammalia, that the 

 muscle moves ; and when there is a regular articula- 

 tion, the distal bone is moved upon the proximal, or 

 one nearest the body, or centre of articulation in the 

 body. In order to make a distinction of these two in 

 the mere naming of the parts to which the muscle is 

 attached, it is usual to say that the proximal attach- 

 ment is the origin of the muscle, and the distal at- 

 tachment the insertion of it ; and when such a muscle 

 acts, the tendency of it is always to draw the point of 

 its insertion towards the point of its origin. If, how- 

 ever, the distal part of the member with which the 

 muscle is connected rests on a fulcrum whose resist- 

 ance is greater than the weight of the animal, the 

 animal must move upon the member, and not the 

 member upon the animal. Thus, in the case of an 

 animal rising from a recumbent or a bent position. 

 or in the case of the straightening of a bent limb by 

 muscular exertion, it is to the body of the animal that 

 the motion is communicated, and the extremity of 

 the straight line remains upon the ground, unless there 

 is as much force in the muscular exertion as to project 

 the animal fairly into the air by a leap. In all leap- 

 ing, galloping, and jumping, and indeed in all kinds 

 of progressive motion, the body of the animal is thus 

 propelled by the action of the muscles against a re- 

 sistance sufficient to overcome the weight or inertia 

 of the animal's body. Thus, the reference to the 

 origin and insertion of muscles applies only to their 

 positions in the body of the animal, and not to the 

 absolute kind of motion which may result from their 

 exercise. 



Sometimes the muscles are inserted directly upon 

 the bones to which they give motion, and in this case 

 a layer of tendinous or cartilaginous matter is the 



means of their union. In the living animal this mat 

 ter adheres firmly ; but when the parts are exposec 

 for a sufficient length of time to the action of boiling 

 water, or even to maceration in cold water, the ten 

 dinous matter is partly converted into jelly and sepa- 

 rates from the bone. In other cases, and indeed ir 

 the majority of cases, in those parts which have exten 

 sive motions, the muscle terminates in a tendon 01 

 cord ; and this tendon, which is popularly callec 

 sinew, consists of substances more or less approaching 

 the nature of ligament. These tendons are fibrous 

 though their fibres are not nearly so distinct as those 

 of the muscles; and they are placed in various direc- 

 tions with reference to the fibres of the muscles them- 

 selves. Those tendons are not susceptible of motior 

 like the muscles, neither are they so elastic as liga- 

 ments ; but there are considerable differences in theii 

 consistency in different animals, and in different parte 

 of the body of the same animals. When the tendon? 

 of a muscle lie in the same direction as the fibres of a 

 muscle itself, they may be at either extremity of the 

 muscle, or at both extremities of it, according to cir- 

 cumstances. The tendons sometimes also pass 

 through the body of the muscles, either in the direc- 

 tion of the muscular fibres or across it ; and sometimes 

 there are several tendons connected with the samt 

 muscle. All these varieties are adaptations to thf 

 different kinds of motion which the muscle is intended 

 to produce ; and not unfrequently the tendon is con- 

 tinued for a considerable way, and over intermediate 

 bones. The muscles of the fingers and toes afford 

 instances of this, for their tendons are very long, thf 

 muscles being situated upon the bones of the fore 

 arm in the case of the fingers, and upon the bones ol 

 the leg in the case of the toes. When the tendons 

 of muscles are extended in this way, they generally 

 pass over bones which modify their motion, and not 

 unfrequently over joints which have proper muscles 

 for their own movements. In these cases the tendons 

 are tied into their places by ligaments which surround 

 them, and keep them to their arrangement ; and very 

 often it is where there are such ligaments, that modi- 

 lying bones, with sliding surfaces, diversify the effect 

 ultimately produced upon the part which the long 

 tendon connects with the muscle. 



In all those muscles which immediately affect the 

 bending of joints, there must be in the greater num- 

 ber of cases an action of muscle against muscle ; and 

 these opposed muscles are called the antagonists of 

 each other ; as, for instance, a muscle which bends a 

 joint, and a muscle which stretches it in the opposite 

 direction, are antagonists, and the first is called a 

 flexor muscle, and the second an extensor. When 

 the bending or contractory action of the part is more 

 vigorous, or, which amounts to the same thing, more 

 important in the action of the animal, the flexor mus- 

 cle is always the stronger ; but when the extension of 

 the part is the chief action, the flexor muscle is the 

 weaker. The muscles in the human body are very 

 numerous, very varied in themselves, and in the kinds 

 of motion which they produce ; but in the case of the 

 individual fibre,the bundle, or the congeries of bundles, 

 of which the several portions are separated from each 

 other by tendinous septa, the action of the muscle 

 is always the same namely, the pulling together of 

 its opposite extremities, by the shortening and swel- 

 ling out of the fibrous part, and the extension of it in 

 length by the subsidence of the contraction, and the 

 relaxing of the muscle and its tendons. 



